The 2nd Mass prepares to take the fight to the invaders with an assault on one of their bases. But Weaver’s increasingly strange behavior worries Tom that he might not be fit to command. Hal and Tom encounter a left-behind woman who employed a suspicious means of surviving the invasion, making it unclear whether they can trust her.

With Weaver leading several squads of fighters against the aliens, Tom remains behind to help protect the civilians as they evacuate. But a major breach in security endangers both the soldiers and the civilians. Tom is confronted with a decision that may lead him to discovering what the aliens want with the captured teenagers, humankind and the planet.

Weaver is still in command of the 2nd Mass, while Anne continues to serve as medic. They have seen many battles and are a much leaner unit now. Pope has taken command of the Berserkers, a renegade group within the 2nd Mass that Weaver doesn’t fully trust.

The 2nd Mass meets new faces, while Tom comes across his former mentor, but it’s difficult to know whom to trust. Maggie realizes that Pope may not be sticking with the group very long. Tector embraces his military past.