Mass Effect: Retribution follows soon after the events of Mass Effect: Ascension. The Illusive Man, leader of the pro-human paramilitary organization Cerberus, is attempting to learn more about the Reapers, an advanced race of sentient machines that periodically purges the galaxy of all organic civilizations. Having obtained Reaper technology, the Illusive Man decides to implant a human with it to learn more about the Reapers. Paul Grayson, a major character in Mass Effect: Ascension and former Cerberus operative, is kidnapped to become the Illusive Man's test subject.