Callisto, converted from one of Jupiter's moons to a giant space station in the greatest human endeavour in history, speeds through empty space on its sixty-year mission to reach the Elysian System, a possible new living space for Earth's population. The occupants of Callisto carry on with their lives and work in the seven connected domes, accustomed to an existence of isolation and routine. Suddenly, a malevolent presence appears in Callisto's complex hardware and software network. People die, victims of apparently malfunctioning systems. Vital data is obliterated by instructions sent from seemingly nowhere. Manufacturing machinery goes haywire. The crew of Callisto, terrified, attempt to carry on as usual. Deputy Security Chief Rey Barrett, an expert in Community Policing and peaceful negotiation and a man of limited network knowledge, is faced with the task of finding and neutralising the evil presence. Accompanied by his inexperienced assistant, Julie, Rey faces more and more vicious attacks on Callisto inhabitants and property as he fights to find and combat the frighteningly able and intelligent villain.