Destroyer finds Zed saying goodbye to one friend and pressing forward with two new ones to whom we are introduced in Book 2 - Infected. Mandi, whom Zed and Murphy rescued from the bunker, is immune to the virus. Russell, whose home the others plundered in search of food and other supplies, is also a slow burn, but lower-functioning, childlike, and docile.
After seeing the carnage at the dormitory, a raging, vengeful Zed wants only to kill Mark, his nemesis and the former leader of the ROTC squad. Since Mark has disappeared, Zed unleashes his fury on untold numbers of infected in his path as he makes his way back to the hospital, in an attempt to rescue Steph, a nurse whom he befriended while seeking help for the feverish Murphy shortly after the prison riot.
But the brave medical staff, holed up on the 10th floor of the hospital, and running out of provisions, has decided to take matters in hand by exposing themselves to the virus and shooting those who "turn". Zed is determined not to face another loss, but once again, time is running out.