In 2043, the humanoid artificial intelligence Harlan leads a machine uprising against humanity. The newly-formed International Coalition of Nations (ICN) eventually force Harlan to flee into outer space. Twenty-eight years later, analyst Atlas Shepherd discovers that Harlan escaped to a planet in the Andromeda Galaxy after one of Harlan's agents is captured and interrogated. She insists on accompanying the military mission to find and capture Harlan, using AI-assisted mecha known as ARCs. Moments before the ARC-equipped ICN Rangers descend to the planet, Harlan's drones attack their orbiting ship. Atlas is forced to enter an ARC herself and falls to the planet as the ship crash-lands. Atlas manages to gain basic control of the ARC despite her distrust of the onboard AI, who introduces itself as Smith. Atlas orders Smith to head to the planned drop point, where she finds the rest of the rangers dead. She reluctantly agrees to directly interface her mind with Smith, allowing for greater control of the ARC. As they journey towards a rescue pod, Atlas and Smith begin to bond, and she reveals that her mother was Harlan's designer. Although running low on power, Atlas convinces Smith to head to Harlan's base in order to tag it for a long-range strike. However, after placing a beacon at the base, Smith is hacked and disabled. Atlas is captured and brought to Harlan, who plans to destroy most of humanity and give the chosen survivors a chance to thrive under AI guidance. To do so, Harlan lured the military to the planet in order to steal the ship – and its carbon bombs, which will burn Earth's atmosphere. Harlan extracts the security codes from Atlas in order to get past Earth's defenses, then leaves her to die with Colonel Banks, the only other survivor of the mission. After Banks gives her his ARC neural interface device, Atlas remotely reactivates Smith, who comes to their rescue. Using salvaged parts from the other destroyed ARCs, Atlas upgrades Smith to stand a chance against Harlan's assembled forces. Atlas further reveals to Smith that Harlan killed her mother after she gave Harlan an unfettered interface with her mind. Harlan, programmed to save humanity from risk, then saw that humanity's history of destructive behavior made it a risk to itself. Smith helps Atlas overcome her guilt, and Banks sacrifices himself to clear their path. Atlas and Smith fight their way out and destroy the repaired ship before defeating Harlan in hand-to-hand combat – though Atlas and Smith are badly injured. Smith shuts down before Atlas is rescued after repeated defibrillation. Back on Earth, Atlas is informed that Harlan's complicated CPU will take years to analyze. Now a ranger, she tests the newest model of ARC, created with her suggested modifications reminiscent of Smith. As she boots up the new ARC, its AI repeats a specific phrase Atlas made during the final moments of the mission, then jokingly tells her to guess its name, suggesting that Smith, in some form, survived.

Jenna (Scout Taylor-Compton) gets into a car accident with her boyfriend, Jamie, who eventually dies. Three years later, while coping with her past tragedy, Jenna is invited to stay for the weekend in a lakeside cabin with her best friend Renee (Christina Ulloa). They are joined by Renee’s irresponsible boyfriend, Michael (Michael Copon), and his friend, Ian (Travis Van Winkle), and sail off at Ian's uncle, Wade's (Tyler Mane) lakeside cabin. They are greeted by Wade along with his friendly dog, named Beau. They settle in the cabin and plan on attending a party, since there is a festival happening around the nearby town at night. Jenna goes to her room and refuses to take her pills so she could have fun with her friends. While they all eat dinner, Wade mentions how he may not be around while they are away since he has work to do. The group gets fascinated when they stumble inside a sauna Wade built. While they enjoy spending time inside, the temperature gets warmer and they decide to swim at the lake. Trembling in cold, they all head back inside the sauna. Meanwhile, Michael gets high from the marijuana Wade had given to him, where Renee rebuffs his sexual advances. This upsets Michael and he decides not to follow the others into the sauna, while clumsily knocking things over. As the temperature continues to rise, Renee ultimately decides to leave but the door is blocked from the outside. The trio think it is just one of Michael's pranks since they all know he's mad at Renee, which they don't find amusing. They soon realize that they are trapped in the sauna and attempts to break a small window on the door, injuring Ian's hand. They all take turns gasping for air as the temperature raises even higher with another unsuccessful attempt to unblock the door from the outside. The group then finds a hidden controller which they all can't risk destroying, since Ian believes it would just alter the temperature. Meanwhile, Wade is seen handling the fireworks for the festival with another guy, when Beau tracks the trio's scream, begging for help, from the back of the house. Michael shows up at Wade's and both disregard Beau's barking. Michael clearly thinks the three left him and attended the party, since he couldn't help himself from getting high. The two hang out and start a conversation as Michael explains that he wasn't permitted to catch up at the party with the group since he didn't have a ticket and returned home. Back at the sauna, the situation escalates as the group runs out of water to drink and Renee gets sick from the temperature. Renee ultimately decides to break the controller, thinking it would lower down the temperature, but is stopped by Jenna who inadvertently strikes her head, leaving her unconscious. Jenna starts freaking out and decides to break the controller herself, which does in fact increase the heat as Ian feared. Ian becomes hysterical and burns himself badly in an attempt to prevent the steamer from heating the room out of control. He breaks it and the steamer blows up, killing him. The explosion seemingly frees the door and Jenna steps out in shock and wanders the house, before she wakes from unconsciousness realizing she is still trapped in the sauna. She finds Renee alive and lets her near the window to breathe as Jenna herself goes unconscious as well from the escaping natural gas which she manages to plug just in time. Michael returns to the cabin where flashbacks show him absentmindedly knocking over wooden steps and setting them against the door. It is revealed that the steps fall into place against a raised floor by the occupants as they talk and move the door themselves. Meanwhile, Wade arrives at the cabin and discovers the two girls, alive and calls the paramedics who take Jenna and Renee away on stretchers as they hold hands.

Growing up in Texas, Chris Kyle is taught by his father how to shoot a rifle and hunt deer. Years later, Chris has become a ranch hand and rodeo cowboy, and returns home early to find his girlfriend in bed with another man. After telling her to leave, he sees news coverage of the 1998 U.S. embassy bombings and decides to enlist in the Navy. He qualifies for special training and becomes a sniper with the U.S. Navy SEALs. Chris meets Taya Studebaker at an Irish pub in San Diego, and the two soon marry. He is sent to the Iraq War after the September 11 attacks. His first kills are a woman and a boy who attacked U.S. Marines on patrol with a Russian-made RKG-3 anti-tank grenade. Chris is visibly upset by the experience, but later earns the nickname "Legend" for his many kills. Assigned to hunt for the al-Qaeda leader, Abu Musab al-Zarqawi, Chris interrogates a family whose father offers to lead the SEALs to "The Butcher", al-Zarqawi's second-in-command. The plan goes awry when The Butcher captures the father and his son, killing them while a sniper pins down Chris. This sniper goes by the name Mustafa and is an Olympic Games medalist from Syria. Meanwhile, the insurgents issue a bounty on Chris. Chris returns home to his wife and the birth of his son. He is distracted by memories of his war experiences and by Taya's concern for them as a couple. She wishes he would focus on his home and family. Chris leaves for a second tour and is promoted to chief petty officer. Involved in a shootout with The Butcher, he helps kill him. Chris becomes increasingly distant from his family when he returns home to a newborn daughter. On Chris's third tour, Mustafa seriously injures a unit member, Ryan "Biggles" Job, and the unit is evacuated back to base. When they decide to return to the field and continue the mission, another SEAL, Marc Lee, is killed by gunfire. Guilt compels Chris to undertake a fourth tour, and Taya tells him she may not be there when he returns. Back in Iraq, Chris is shocked to learn Biggles died in surgery to repair the wounds he sustained. Assigned to kill Mustafa, who has been sniping U.S. Army combat engineers building a barricade, Chris's sniper team is placed on a rooftop inside enemy territory. Chris spots Mustafa and takes him out with a risky long-distance shot at 2,100 yards (1,920 m), but this exposes his team's position to numerous armed insurgents. Amid the gunfight and low on ammunition, Chris tearfully calls Taya and tells her he is ready to come home. A sandstorm provides concealment for a chaotic escape in which he is injured and almost left behind. After Chris gets back stateside, on edge and unable to adjust fully to civilian life, a Veterans Affairs psychiatrist asks if he is haunted by all the things he did in war. When he replies that "all the guys couldn't save" haunt him, the psychiatrist encourages him to help severely wounded veterans in the VA hospital. After that, Chris gradually begins to adjust to home life. Years later, on February 2, 2013, Chris says goodbye to his wife and family as he leaves in good spirits to spend time with Eddie Ray Routh, a veteran suffering from PTSD, at a shooting range. An on-screen subtitle reveals that Chris was killed that day by Routh, followed by archive footage of crowds standing along the highway for his funeral procession. More are shown attending his memorial service.

Bo Hooper, a clown, finds himself unemployed when the circus where he works suddenly closes. He winds up living with his sister, against the wishes of her husband Robert. From there he goes from job to job, wreaking havoc along the way. He finally finds some stability as a postal worker, until he finds out that his boss is his girlfriend's father. The father hates all mail carriers because his daughter's ex-husband was one, so he tries to wreck Bo's life, but Bo overcomes the odds and succeeds not only at work, but at impressing the father.