Seventeen-year-old Zach was visiting his uncle in a small Montana town when a mysterious illness ripped through the world. Most died, but those who survived the Infection became mindless killers, spreading the disease with a single scratch. Now, a year later, civilization lies in ruins, and Zach is the town's sole survivor. Desperately lonely, he longs to return to his family in Seattle, but his fears hold him captive.

Eighteen-year-old Aiden is on a critical mission for the covert Scientific Collective, delivering vials whose contents could cure the Infection. Tortured by his boyfriend's death, he welcomes the risks of the perilous journey. When a militia attacks Aiden, he flees to Zach's town.

The boys escape together and soon form a bond as they comfort each other in this desolate and broken world. The farther they travel, the more their affection grows, as do the forces pulling them apart. But their greatest threats are the secrets they keep. Zach hides details of his uncle's death, and Aiden conceals the vials' sinister origins. In order to survive, they'll have to confront the truths that could tear their love apart.