While treating a seriously wounded B.A., a suspicious small town doctor notifies the sheriff, who fears that B.A. may be part of a biker gang returning to free its jailed leader.

Deep space, some time in the future. Still following the Black Guardian's orders, Turlough sabotages the TARDIS, forcing an emergency fusion with an apparently deserted starship. But the ship is headed for the notorious plague colony, Terminus. Surrounded by plague victims and space pirates, is the Doctor too preoccupied to notice the greatest threat of all - a threat connected to the position of Terminus at the exact centre of the universe?