Charles Bowen is a immigration officer with a difference: the migrants he deals with don't come from other countries but from other universes. Known as shifters, they materialize from parallel timelines, bringing with them a mysterious drug called slip which breaks down the boundary between what is and what might have been, and offers the desperate and the dispossessed the tantalizing possibility of escape.Summoned to investigate a case at the Thurston Meadows Social Inclusion Zone, Bowen struggles to keep track of his place in the world and to uphold the values of the system he has fought so long to maintain ...