While most of the landscape is destroyed by nuclear warheads, Strand thrives in one of the few inhabitable places left; Strand's search for survivors uncovers a stranger with an unexpected connection to his past.

As Morgan, Grace and Mo struggle to adapt to life on the submarine, a food shortage forces them to face the nuclear fallout outside the sub.

Against the advice of the group, Sarah searches for Wendell, and in the process encounters a dangerous survivor who forces her to take part in a search of his own.

With a code to guide them, Dwight and Sherry become ethical outlaws known as the Dark Horses. When Strand recruits them for a search and rescue mission, it forces them to question their code and their future.

Morgan searches for Al, only to discover that he's not the only one looking for her, and that his search may have put a target on his own back.

When baby Mo gets sick, Morgan successfully pleads for entry into Strand's Tower. Morgan quickly learns even Strand's benevolence has its limits.

Alicia enlists Morgan's help to search for a new home for her people, but Morgan soon learns the search is more complicated than he imagined.

Alicia takes refuge in the home of a mysterious stranger. With her fevers growing worse and Arno pursuing her at every turn, Alicia is forced to confront the failings of her past and how she will face her future.

When Charlie shows up at the Tower unexpectedly, Howard recruits a young Ranger in training to determine the reason for her visit; as they journey beyond the Tower together, Charlie's true motives are revealed.

Luciana and Wes test the limits of their patience when Daniel’s worsening mental state ends up endangering them all.

When baby Mo goes missing inside the Tower, Dorie Sr. finds himself in a unique position to prove his worth to an increasingly paranoid Strand.

Morgan and Alicia plan their next steps; Dwight and Sherry face the prospect of having to choose between their code and their safety.

As the battle for the Tower heats up, Alicia brings the fight to Strand's front door.

As the survivors prepare to escape the area by raft, Alicia turns back to save one more person trapped in the fallout.

Morgan finds a new ally who turns out to be more trouble than he bargained for.