After a harrowing escape from a battlefield of warring camps, Lance and Cass have reunited their friends and family. They've taken refuge in The Light, possibly the only building left in the world with electricity.

But their problems have just begun.

Each night, creatures ascend from Baltimore's sewers, swarming the building and testing the defenses for weaknesses. These aren't the monstrosities Lance and Cass first encountered years earlier—they've evolved. Their laments fill the darkness like a primitive language. A leader has emerged from the hordes, guiding the infected in their assaults on the remaining humans.

With opposing factions of survivors attacking them by day, and legions of the nightmarish horrors prowling through the night, Lance and Cass must make an uneasy alliance with The Light's residents to defend their loved ones.