Frank clashes with Charlie to protect Babbit, who has become the subject of an investigation.

Frank seeks medical answers; Charlie and Helen travel to survey an off-site reactor.

Both Charlie and Frank face serious questions as to the future of their projects.

A development overseas re-invigorates the hunt for a spy on The Hill. Charlie and Abby make a sacrifice when the plan with Frank is threatened.

Akley becomes vulnerable when he tries to fix Thin Man's shortcomings.

Charlie is forced into a new leadership role in the race to build the world’s first atomic bomb.

Liza faces off against Darrow as Abby learns a secret about Oppenheimer.

Frank attempts to navigate his new place on the Hill.

The scientists and the Army battle for control of the bomb.