In the world of 2116, a person's maximum age is strictly legislated: twenty one years, to the day. When people reach this Lastday they report to a Sleepshop in which they are willingly executed via a pleasure-inducing toxic gas. A person's age is revealed by their palm flower crystal embedded in the palm of their right hand that changes color every seven years, yellow (age 0-6), then blue (age 7-13), then red (age 14-20), then blinks red and black on Lastday, and finally turns black at 21.

Runners are those who refuse to report to a Sleepshop and attempt to avoid their fate by escaping to Sanctuary. Logan 3 is a Deep Sleep Operative (also called Sandman) whose job is to terminate Runners using a special weapon called the Gun, an unusual revolver which can fire a number of different projectiles. Runners are most terrified of one called the Homer which homes in on body heat and deliberately ignites every pain nerve in the body, killing the target. Sandmen practice Omnite, a fictional hybrid martial arts style. On his own Lastday, Logan becomes a Runner himself in an attempt to infiltrate an apparent underground railroad for runners seeking Sanctuary-a place where they can live freely in defiance of society's dictates. For most of the book Logan is an antihero; however, his character develops a sympathy towards Runners and he becomes more of a traditional hero figure.