Peggy is contacted by old acquaintance Howard Stark when he is framed for unleashing his deadliest weapons and can trust no one else. To help Peggy clear Stark's name, he insists his butler, Edwin Jarvis, be at her beck and call - whether she likes it or not. But the risk is great: If caught, Agent Carter could be targeted as a traitor and spend the rest of her days in prison... or worse.
Peggy closes in on the thief who took Stark's bomb formula, only to discover that he is part of a worldwide conspiracy group calling themselves Leviathan. Meanwhile, SSR discovers evidence tying Stark to the destruction of Roxxon.
The SSR trace the explosion at Roxxon to Edwin and bring him in for interrogation. While trying to protect her friend, Peggy learns that Edwin has secrets of his own.
Despite the SSR manhunt, Howard smuggles himself into New York City and asks Peggy to steal back one of his inventions from the SSR lab. However, Peggy soon discovers that Howard has an ulterior motive. Meanwhile, Daniel tries to track down the mysterious blonde woman, while Dottie reveals an unexpected side to her personality.
Peggy convinces her superior to let her go on a mission to Russia with Jack, as long as she can recruit the Howling Commandos to help them. She does and they find a scientist who may hold the key to Leviathan's plans.
Peggy discovers the shocking truth about Leviathan but doesn't realize that her true enemies are even closer than she imagined. Meanwhile, Souza is close to confirming the truth about Peggy and may just put her in the crosshairs of the SSR.
Peggy is cornered and more vulnerable than ever as Leviathan makes their move against her. As the SSR zeroes in on Howard Stark, they may pay the ultimate price as they find their true enemy is closer than they realized.
The SSR learn what Ivchenko is up to, while the Russian abducts Howard and plans to use him in his plan for revenge.