Robbins is sent to prison for the assassination of his general officer, a prison you only get out of when you die. Since nobody ever gets out of the prison, nobody knows how the prison is like. The prison manager has realized this and bought himself an island (playground) called "Absolom" where the worst prisoners are let lose to create an isolated barbaric society where the strongest men rule - a living hell. This is where Robbins is dropped off after he almost kills the prison manager.
