During the Great Fire of Rome in AD 64, Emperor Nero "fiddles". Tigellinus informs Nero that he is suspected of starting the fire. Nero instead has the fire blamed on the Christians. In Rome, the Apostle Titus, Mercia, and Favius are apprehended by a mob for being Christians. Marcus Superbus, the prefect of Rome, arrives and disperses the mob, allowing the Christians to go free. News of Marcus's mercy towards the Christians spreads throughout Rome, including to Empress Poppaea. At a fountain, Marcus meets with Mercia again; there, Licinius reads Nero's edict to Marcus reminding him of his duty to arrest Christians. Later that night, Titus sends Stephan, a young Christian man, to tell other Christians of the secret meeting at the Cestian Bridge. Shortly after, Marcus arrives at Mercia's home wanting to take her for himself, but Mercia decides to stay. Stephan is arrested by Licinius under suspicion of being a Christian. In a dungeon, under torture Stephan reveals the location of the Christians' secret meeting. After learning of Stephan's arrest and torture, Marcus races to the meeting hoping to save Mercia. Along the way, he crashes into Poppaea's carriage. She demands Marcus stay, but he leaves her and promises to be with her in the morning. At the meeting, Roman soldiers surround the Christians, and Titus and some members of his congregation are struck dead by arrows. Marcus arrives at the meeting and saves Mercia, and takes her home, while the other Christians are arrested and imprisoned. The next morning, Poppaea scolds Marcus for his affections to Mercia. Elsewhere in the palace, Tigellinus informs Nero of Marcus's disobedience to his edict. Nero accuses Marcus of betrayal. Jealous of Mercia, Poppaea influences Nero to sign an order for Mercia's arrest. At a feast in Marcus's home, he introduces Mercia to Ancaria, who performs an exotic dance. Outside, Ancaria's performance is drowned out by the Christians' singing. Annoyed by the singing, Marcus sends his party away so he may be alone with Mercia. He tries to get Mercia to renounce her Christian faith so she may be with him, but she refuses. Shortly after, Licinius arrives to arrest Mercia, who is to be executed for treason amongst one hundred Christians in the arena. Marcus returns to Nero's palace and demands that the emperor spare Mercia, but Nero refuses. In the arena, the audience is entertained by several spectacles, including gladiator battles. When the time for the Christians' execution arrives, Mercia is told to stay behind by Poppaea's orders, as she is to be executed alone. In the arena, the Christians are mauled to death by lions. Following the execution, Marcus again asks for Mercia to renounce her faith and be his wife. Mercia refuses once more, but she states that she loves him. Refusing to live without her, Marcus accompanies Mercia, and they are both executed.

Late one evening, Allan Gray, a wandering student of the occult, arrives at an inn close to the village of Courtempierre, France, and rents a room. He is awakened from his sleep by an old man, who enters the locked room and leaves a small rectangular package on the table with "To be opened upon my death" written on the wrapping paper. Feeling drawn to investigate, Gray takes the package and leaves the inn. Gray follows the shadow of a soldier with a peg leg to a disused factory, where he sees the shadow reunite with its body, and witnesses other shadows dancing. He also sees an old woman who seems to hold sway over the shadows, and encounters an old man with a mustache, who shows Gray the door. Following some more shadows to a manor house, Gray looks through one of the windows and sees the lord of the manor, who is the man who gave him the package, get shot by the shadow of the soldier. Gray gets the attention of an old servant, and they rush to the lord of the manor, but it is too late to save him. Giséle, the lord of the manor's younger daughter, is there when he dies, but her sister, Léone, does not leave her bed, as she is gravely ill. A coachman is sent to get the police, and the old servant's wife invites Gray to stay the night. In the library, Gray opens the package and finds a book inside about horrific demons called vampires. As he begins to read about how the creatures suck blood and gain control over the living and dead, Giséle says she sees Léone walking outside. They follow her, and, when they catch up, see the old woman from the factory bent over Léone's unconscious body. The old woman slinks away, and Léone, who is discovered to have fresh bite wounds, is carried back to bed. The carriage returns, but the coachman is dead. The village doctor visits Léone at the manor, and Gray recognizes him as the old man with a mustache that he saw in the factory. The doctor tells Gray that Léone needs a blood transfusion, and Gray agrees to donate his blood. Exhausted from blood loss, Gray falls asleep. Meanwhile, the old servant has noticed the book and begun to read it. He learns that a vampire can be defeated by opening its grave at dawn and driving an iron bar through its heart, and that there are rumors that a vampire was really behind a previous epidemic in Courtempierre, with a woman named Marguerite Chopin being the prime suspect. Gray wakes up sensing danger and rushes to Léone's bedside, where he stops her from drinking poison that the old woman had the doctor bring to the manor. The doctor flees, kidnapping Giséle, and Gray follows. Just outside the factory, Gray trips and has an out-of-body experience, in which he sees himself dead, sealed in a coffin with a window, and carried away to be buried. After his spirit returns to his body, he notices the old servant heading to Marguerite Chopin's grave. They open the grave and find the old woman perfectly preserved, until they hammer a large metal bar through her heart, at which point she becomes a skeleton. The curse of the vampire is lifted, and, back at the manor, Léone suddenly recovers. The ghost of the lord of the manor appears to the doctor, causing him to run away and the soldier to fall to his death down a flight of stairs. Using information he gathered during his out-of-body experience, Gray finds and unties Giséle. The doctor tries to hide in an old mill, but the old servant, seemingly aided by an unseen force, locks the doctor in a chamber where flour sacks are filled and activates the mill's machinery, which fills the chamber with flour and suffocates the doctor. Giséle and Gray cross a foggy river in a boat and find themselves in a bright clearing.

On a foggy night in 1850, Mary Rutledge and retired Colonel Marcus Aurelius Cobb arrive in San Francisco Bay aboard the clipper ship Flying Cloud. She had come to wed a wealthy owner of a gold mine, but he had lost his mine at the roulette wheel when the ball landed on red 13 times at the Bella Donna, a gambling house and restaurant. The men at the wharf reluctantly inform her that her fiancé is dead, murdered most likely by Louis Chamalis, the powerful owner of the Bella Donna. Mary is upset, but quickly pulls herself together. Mary meets Chamalis and goes to work for him. Chamalis gives her the name "Swan" and showers her with extravagant gifts. Their relationship sours quickly because Swan is angered by Chamalis's destructive power-mongering. She does not, however, mind running a crooked roulette wheel and cheating the miners out of their gold. Colonel Cobb purchases a printing press, with the intention of starting a respectable newspaper for the people of San Francisco. His first issue includes an article criticizing an unpunished murder by Chamalis and his men. When Chamalis finds out, he threatens to destroy Cobb's printing press and burn down the building, but is halted by Swan. Chamalis demands that Cobb never print anything attacking him. The colonel unwillingly complies. Swan becomes disillusioned with her life in San Francisco. Her distant behavior irks Chamalis. One morning, she sets out on horseback. When it begins to rain heavily, she seeks refuge in a seemingly abandoned cabin, where she meets poet and gold miner Jim Carmichael. Swan is taken with him, but lies about her current situation after hearing his criticisms of the city. He gives her his book of poems as a memento. Carmichael decides to return to New York. Because of fog, the ship will not leave for a few days. He meets Chamalis's helper, Old Atrocity, who, seeing his bags of gold is happy to show him to the Bella Donna. Carmichael is surprised to find Mary working there. He is served drugged liquor and plays roulette at her table. He loses his composure, insults Swan and eventually loses his money. Carmichael wakes the following morning in the Bella Donna's kitchen. His eloquent speech impresses Chamalis, who hires him on the spot as a waiter. Carmichael's presence bothers Mary, who offers him money to depart. Carmichael refuses, wishing to earn the fare on his own. Cobb puts up a poster telling about a murder Chamalis ordered and how the Bella Donna cheats customers. Seeing it, Chamalis's henchman "Knuckles" Jacoby shoots both the man who put it up and the publisher when he tries to defend him. Dying, Cobb orders his assistant to print the truth. Vigilantes hang Knuckles. Devastated by Cobb's death, Mary acknowledges her love for Carmichael, and works the roulette table so that he wins back the gold he lost. Chamalis finds out and sets out to kill Carmichael. The lovers decide to leave together. They find a rowboat and attempt to board the ship in the harbor. They have trouble seeing in the fog, but can hear Chamalis pursuing them. He shoots and injures Carmichael, and corners them beneath a pier. Mary begs him, as proof of his love for her, not to kill Carmichael. Chamalis agrees, but tells her he does not want her anymore. The sheriff arrives with a mob, and Chamalis allows himself to be taken away. Mary returns to Carmichael's side aboard the ship as it prepares to set sail.

The film's plot is centered on an engineer Jim Ripple who invents universal robots to help workers, being himself from a workers' family. He theorizes that cheap production will make all goods so cheap that Capitalism will fall. The workers do not share his view and his family considers him a traitor. A key element of his invention is a high-capacity capacitor that powers the robots. The government becomes interested in the invention because the robots can be used as a weapon as well. Ripple is given a top secret factory and funding so that he can produce robots. The robots are not autonomous or intelligent, and controlled either by radio or by sound, for which purpose Ripple uses a saxophone. When drunk he even makes the robots dance. At a day of a universal workers' strike, the administration of a factory where the Ripple's brother works, located in the same town where the robot producing plant is located, replaces workers with robots. A workers' delegation visits the factory to see that there are no strike breakers, and finds that actually it is the robots who do the work. The meeting ends with an accident when Ripple tries to show the abilities of a robot to the workers; in an accident, one of the workers dies. This sparks a conflict between workers and the plant administration assisted by the military. The military decides to use robots against the workers as a weapon. The robots are commanded by an officer sitting in a tank using a radio remote control device. Trying to prevent the hostilities Ripple tries to stop the robots with a saxophone, but he is unsuccessful and is killed. Finally the workers gain control over the robots with their own remote control device, which they had covertly assembled before, making necessary measurements on the robot assembling factory and researching the Ripple's prototype robot "Micron", whom he left damaged at his home.

American dancer Jerry Travers comes to London to star in a show produced by the bumbling Horace Hardwick. While practicing a tap dance routine in his hotel bedroom, he awakens Dale Tremont on the floor below. She storms upstairs to complain, whereupon Jerry falls hopelessly in love with her and proceeds to pursue her all over London. Dale mistakes Jerry for Horace, who is married to her friend Madge. Following the success of Jerry's opening night in London, Jerry follows Dale to Venice, where she is visiting Madge and modelling/promoting the gowns created by Alberto Beddini, a dandified Italian fashion designer with a penchant for malapropisms. Jerry proposes to Dale, who, while still believing that Jerry is Horace, is disgusted that her friend's husband could behave in such a manner and agrees instead to marry Alberto. Fortunately, Bates, Horace's meddling English valet, disguises himself as a priest and conducts the ceremony; Horace had sent Bates to keep tabs on Dale. On a trip in a gondola, Jerry manages to convince Dale and they return to the hotel where the previous confusion is rapidly cleared up. The reconciled couple dance off into the Venetian sunset, to the tune of "The Piccolino".

A group of wealthy industrialists gather at the home of Mr. Lloyd, a millionaire who introduces them to Richard "Mack" McAllan, the engineer who successfully spearheaded the construction of the Channel Tunnel (the story takes place in the unspecified near-future, though it is noted in the film that the Channel Tunnel is built "in 1940") and so is the Bahamas-Miami tunnel. McAllan informs the group that the "Allanite steel" he developed, along with a "radium drill" developed by his friend Frederick "Robbie" Robbins, makes it possible to construct an undersea tunnel linking England with the United States. Though the group is initially skeptical, the backing of Lloyd and his associate Mostyn convinces the group to buy shares in the project. Three years into construction of the tunnel, McAllan is a worldwide celebrity, but his work keeps him from his devoted wife Ruth and their young son Geoffrey. Called away to New York, he is informed that the people are losing faith in the project. Lloyd needs to have him use his fame to get support. Lloyd's attractive daughter Varlia, who is secretly in love with McAllan, keeps him company to intensify the attention of the press. The photos of the couple add to Ruth's sense of isolation, and she decides to work in the tunnel as a nurse. There she is affected by an unknown gas afflicting the workers and loses her eyesight. Worried that her husband no longer loves her and not wanting him to stay with her out of pity, Ruth leaves McAllan, taking their son with her. Heartbroken at her unexplained departure, McAllan throws himself into the project, alienating Robbins in the process. Years pass. Though the cost of the tunnel in lives and money continues to mount, the British prime minister and American president eagerly anticipate its completion and the unity and peace they promise it will bring. Ruth lives in the countryside with her now-grown son, who lobbies Robbins to find him a job working in the tunnel. The tunnel is nearing completion, but the workers encounter a submarine volcano that will necessitate a detour. McAllan needs more money to establish a detour, but is opposed by Grellier, an arms manufacturer, and Mostyn. The two men earlier manipulated the stock market to become the controlling shareholders in the company. Lloyd suspects that Grellier and Mostyn plan to use the delay to depress stock prices again, and this time gain total ownership of the tunnel. However, Varlia convinces Mostyn to fund further construction by promising him the one thing he has always wanted, but never gotten: her hand in marriage. Though the project goes forward, Grellier has Mostyn killed for backing out of their deal. Despite the renewed effort, samples indicate the volcano may be too large to drill around. The drill breaks through to volcanic gases that kill hundreds of workers, including Geoffrey. The project seems on the verge of collapse. Determined to see the project through and fortified by the reappearance of Ruth (who came to the tunnel site to discover Geoffrey's fate), McAllan vows to continue. With three volunteers, McAllan and Robbins man the radium drill, and despite near-fatal temperatures, break through to the American side of the tunnel.

Marion Dixon, a popular white American circus artist, is forced to flee for her life with her black baby to escape a lynch mob in a rural American town. The fate of the black father of her child is not mentioned, but it is heavily implied that he was lynched. Dixon is taken under the wing of Franz von Kneishitz, a sinister German theatrical agent whose mustache and mannerisms resemble those of Adolf Hitler. Kneishitz blackmails Dixon into becoming his lover while exploiting her. Dixon is only kept alive by her love for her son Jimmy, and when she plays in Moscow as a guest performer, she is portrayed as spiritually broken. At the Moscow circus, the circus director Ludvig hires the Arctic explorer Ivan Petrovich Martynov to design a new circus act to top Dixon's "Trip to the Moon" act. Ludvig's fiery daughter Rayechka has a tempestuous relationship with her boyfriend Skameikin. Despite his mission to design an act better than her act, Martynov and Dixon fall in love, which attracts Kneishitz's rage and he beats Dixon quite savagely with his whip. Dixon wants to stay in Moscow with Martynov, saying she has found happiness again. Kneishitz diverts a love letter from Dixon meant for Martynov to Skameikin, which throws the circus into romantic chaos as Rayechka is furious with Skameikin while Martynov is heartbroken. To escape Rayechka, Skameikin accidentally runs into a lion cage and has to calm the lions with a bouquet of flowers. When Martynov does not respond to her love letter, Dixon nearly leaves Moscow with Kneishitz. By this time, Rayechka has learned the truth and she helps Dixon escape Kneishitz. Martynov and Dixon are late to the circus, forcing Ludvig to perform the top act of 1903, the chudo tekhniki ("miracle of technology"), to amuse the impatient audience. Finally, Martynov and Dixon arrive and perform their "Trip to the Stratosphere" act together. Kneishitz interrupts the act to tell Dixon to come with him or else he will reveal her secret. When she refuses, Kneishitz delivers a Hitler-like rant about how Dixon has a black son called Jimmy, only for the audience to laugh at him. Ludvig tells Kneishitz that the peoples of the Soviet Union do not share his concern about racial purity or race at all. Dixon's black son is embraced by friendly Soviet people. Kneishitz tries to seize Jimmy, but the audience unites to save him. Finally, a group of burly Red Army soldiers in the audience block Kneishitz, who cowers in fear and leaves. The movie climaxes with a lullaby being sung to the baby by representatives of various Soviet ethnicities taking turns. The lyrics of the lullaby to Jimmy are sung in Russian, Ukrainian, Yiddish, Uzbek, and Georgian. One of the members of the audience is a black American man dressed in a Soviet naval officer's uniform with a white Russian wife, which was meant to show that there is no racism in the Soviet Union. The lyrics of The International Lullaby declare: " Son prikhodit na porog/Krepko, krepko spi ty/Sto putei, sto dorog/Dlia tebia otkryty " ("Sleep comes to your doorstep/Sleep very, very soundly/A hundred paths, a hundred doorways/Are open to you"). Dixon and Martynov declare their love for one another while Rayechka and Skameikin become engaged. The film ends with Rayechka and Dixon marching together in the annual May Day parade under banners depicting the faces of Lenin and Stalin.

Irene Vail decides to divorce her husband, the rich ship owner Bruce Vail. However, Bruce learns that he can prevent the divorce if he can provide evidence that she has been involved with another man. He pays his driver Michael to visit Irene's hotel room in Paris and pretend to be her lover so that a private detective can catch them in a compromising position. However, a man overhears Irene's startled cry upon finding Michael in her room, and a struggle ensues when the man defends Irene, leaving Michael on the floor, unconscious. When Bruce and the detective burst into the room, the man threatens them with a gun, demands Irene's jewelry and takes Irene hostage. Once they are away, the intruder, Paul Dumond, returns Irene's jewelry and invites her to dine with him at the Château Bleu restaurant, where he works as a waiter. They dance and Irene falls in love with him. In the morning, Irene returns to find Vail and the police in her room, as Michael is dead. Vail leads her to believe that Paul is responsible for the murder and blackmails her into coming back to the United States with him in exchange for Paul's freedom. Distraught that he is unable to find Irene, Paul learns that Irene has reunited with her husband and left for the U.S. Sensing something is wrong, he embarks for the U.S. to find her, accompanied by Cesare, his good friend and head chef of Château Bleu. In Manhattan, Paul and Cesare rehabilitate a restaurant, hoping that it will attract Irene. The reunion takes place at last, but Paul learns that Michael is dead and that a man has been arrested in Paris for the murder. Unwilling to let an innocent man pay for what he thinks is his crime, Paul embarks for Paris, and Irene joins him. They travel on the liner Princess Irene, which is owned by Vail and named after her. Vail learns that they are on the ship. In a rage, he orders the captain to travel at full speed, despite the danger of collision with an iceberg, claiming a desire to break the record for fastest crossing. Vail actually hopes that the ship will sink, killing Paul and Irene. The ship does strike an iceberg, and premature news reports state that the ship has sunk with tremendous loss of life. Consumed by guilt, Vail commits suicide and confesses to killing Michael in a note. However, the ship's bulkhead doors contain the water and prevent the ship from sinking. Paul, Irene and the other passengers rejoice when they hear that they are to be rescued.

An army of the Teutonic Order invades and conquers the city of Pskov with the help of the traitor Tverdilo, and massacres its population. Novgorod is their next intended target. Despite resistance from the boyars and merchants of Novgorod (urged on by the monk Ananias, Tverdilo's henchman), an appeal is made to Alexander Yaroslavich Nevsky, to again become their prince and defend Novgorod. To do so he rallies the common people of the Novgorod area. In the decisive Battle of the Ice, on the surface of frozen Lake Chudskoe, the Teutonic forces are defeated. Pskov is retaken, and there Nevsky passes judgment: the surviving Teutonic foot-soldiers are set free, while the surviving Teutonic knights will be held for ransom. Tverdilo the traitor, together with a Catholic priest who blessed the burning alive of Pskov children, disappear as they are mobbed by the onlookers. A subplot throughout is the rivalry and friendship of Vasili Buslai and Gavrilo Oleksich, two famous (and historic) warriors of Novgorod. Both become commanders of the Novgorod forces, and are engaged in a contest of courage and fighting skill in order to decide which will win the hand of Olga Danilovna, a Novgorod maiden whom both are courting. At the same time Vasilisa, daughter of a boyar of Pskov killed by the Teutons, joins the Novgorod forces as a soldier. She and Vasili wind up fighting side by side; she throws him a weapon when he is surrounded and weaponless, and it is she who finds and slays Ananias. Gavrilo and Vasili are seriously wounded and are found by Olga, who retrieves them from the battlefield. Though they defer to each other, in the end Vasili publicly states that neither was the bravest in battle: that honor goes to Vasilisa, followed by Gavrilo. Thus Gavrilo and Olga are united while Vasili chooses Vasilisa as his bride-to-be (with her unspoken consent).