Set in the 1960s, Deathloop takes place over the course of a single repeating day on the subarctic island of Blackreef. First charted in 1931, Blackreef was originally home to a small fishing settlement and a military base where experiments were conducted on local temporal anomalies. It is now owned by the AEON Program, founded by scientist Egor Serling to exploit the island's unique properties to gain immortality by living in an infinite time loop. Serling attracted eight other eccentric and talented individuals to his cause, the Visionaries, and scores of young, fanatical followers called Eternalists dedicated to serving them. Thanks to the time loop, the members of the AEON Program are able to hold a never-ending party where they can do anything they desire without fear of consequences, since the loop resets at midnight and restores everyone to their original state with no memories of the previous day. Disrupting the natural flow of the loop are two of the Visionaries: Colt Vahn and Julianna Blake. Julianna is immune to the time loop's memory erasure, and every day she alerts all of Blackreef's inhabitants that Colt has betrayed the AEON Program and wants to break the loop, causing everyone to hunt him. Colt develops the ability to retain his memories from previous days as well, and is thus able to learn the behaviors and patterns of the Visionaries and Eternalists. In order to break the loop, Colt must assassinate the other eight Visionaries, including Julianna, in one day, since the Visionaries lives keep the loop operating, allowing it to continue resetting at the stroke of midnight, as all of them dying in one loop will result in it destabilising.