The game is set in the year 2084, in a futuristic version of Paris called Neo-Paris. The Memorize corporation has invented a new brain implant called the Sensation Engine (Sensen), which enables roughly 99% of the population to upload and share their memories on the net, as well as remove unhappy or unpleasant memories.
This gives Memorize an immense degree of control over the population and enables them to establish a surveillance state. This, in turn, leads to a small group of rebels forming under the name "Errorists": their mission is to bring down Memorize. The invention of the Sensen has also resulted in the creation of Leapers; memory-addicted humans who have absorbed so many memories that their Sensen has degraded and they have mutated into a subhuman form, now living in the sewers of Neo-Paris.