The novel is divided into three parts, or books. The first is titled "Captain Trips" and takes place over nineteen days, with the escape and spread of a human-made superflu (influenza) virus known formally as "Project Blue", but most commonly as "Captain Trips". The virus is developed at a U.S. Army base, where it is accidentally released. While the base tries to shut down before any infected person can escape, a security malfunction allows a guard and his family to sneak out. Unfortunately, they are already infected, and set off a pandemic that kills an estimated 99.4% of the world's human population, as well as that of domesticated animals, such as horses and dogs.