Watch Marvel's Agent Carter Season 1 in Australia

When Howard Stark finds himself being framed, he reaches out to Peggy to help him clear his name, empowering his butler to help her as needed.

When Howard Stark's deadliest weapon falls into enemy hands, Carter is the only one who can get it back.

As Agent Carter gets closer to Stark's stolen technology, her secret mission could be unraveled by an SSR arrest.

Howard Stark suddenly returns, possibly creating more trouble for Peggy. Chief Dooley follows a new clue that threatens Peggy's future at the SSR.

Carter decrypts an encoded message, received from Leviathan through Demidov's typewriter, for the SSR, learning that Stark will be selling weapons to Leviathan at a Soviet military complex. Thompson is sent to stop the sale and apprehend Stark, and is forced to take Carter when she enlists the help of her war comrades, the Howling Commandos. They discover that young girls are trained at the complex to infiltrate the US as sleeper agents, and realize that they have walked into a trap when one girl kills the Commando Junior Juniper. Soviet soldiers attack the team and Thompson freezes under fire, but Carter ensures that they escape, along with imprisoned psychiatrist Dr. Ivchenko. Meanwhile, Underwood, who is actually a sleeper agent trained at that complex, discovers the photos of Stark's weapons in SSR custody when searching Carter's apartment, while Sousa realizes that Carter is the woman who has been interfering with the SSR's investigation.

Carter and Jarvis investigate the women that Stark has been involved with over the last six months, believing that a female Leviathan operative may have been used against Stark and to kill Krzeminski, but their search is unsuccessful. Sousa reveals to Dooley that Carter is an apparent traitor, and all agents are tasked with tracking her down. They eventually corner her and Jarvis, but Carter fights them off. During the commotion, Dr. Ivchenko, who is actually working for Leviathan, hypnotizes Agent Yauch, who reveals that only Dooley can access Stark's weapons. Yauch shows Ivchenko how to get out of the SSR, before Ivchenko forces him to commit suicide. Carter retrieves Rogers' blood from her apartment. As she tries to escape the building, she is knocked out by Dottie Underwood, but not before realizing that Underwood is the Leviathan operative. Underwood is about to kill Carter when Thompson and Sousa arrive. She feigns ignorance, and the agents arrest Carter.

As Carter is resisting interrogation at the SSR, Jarvis appears with a fake signed confession from Stark, promising surrender if Carter is released. Carter sees Ivchenko communicating in Morse code with Underwood, and reveals the truth about her own investigation to her colleagues to gain their trust. Ivchenko hypnotizes Dooley and has him steal one of Stark's weapons from the SSR's labs: a gas cylinder that Underwood and Ivchenko activate in a crowded cinema before leaving and locking the door behind them. The agents find Dooley wearing a Stark experimental vest given to him by Ivchenko, which Jarvis explains will explode with no way to deactivate it. Dooley jumps out a window moments before the device detonates, killing him but saving the others. The gas in the cinema makes many in the audience become maniacal and attack each other violently, and when an usher arrives soon after, the entire audience is dead.

The SSR discovers the gas cylinder in the cinema and realize that Ivchenko possibly plans to turn all of New York on itself. Stark returns and explains that he had developed the gas, named Midnight Oil, to give American soldiers extra stamina during war, but it caused psychosis and lead to them killing each other. During World War II, the American military stole Midnight Oil and used it on the Soviets at Finow. Stark believes that Ivchenko – real name Johann Fennhoff – blames Stark for the ensuing massacre, and allows the SSR to use him as bait to draw Leviathan out. This plan goes awry when Underwood distracts the agents while Fennhoff kidnaps Stark, and uses hypnosis to convince him to drop the gas on Times Square. At Stark's secret plane hangar, Sousa apprehends Fennhoff while Carter defeats Underwood (who escapes) and convinces Stark not to drop the gas on the city.