Everyone struggles desperately to live the destruction that is approaching on their own terms.

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.

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

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.

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.