The overall plot of the franchise focuses on a puzzle box, the Lament Configuration. It opens a gateway to the Hell-like realm of the Cenobite lifeforms. The Cenobites are an order of former humans who have become monsters who harvest human souls to torture in their sadistic experiments.
Infection is the second (chronologically the third) Exo Zombies map featured in Call of Duty: Advanced Warfare. This map takes place at an Atlas command center centered near a Hoard More storage facility, a Value Voltage gas station, a sewer, and a Burger Town restaurant, which are all overrun by Zombies.