Sabotage! The TARDIS is breaking up! Thanks to the combined efforts of the treacherous Turlough and his evil master, the Black Guardian, the Doctor and his companions are in terrible danger. The outside world has begun to break through and Nyssa has disappeared.

Can the TARDIS' fail safe mechanism save them all by docking with another ship? Unlikely, when the nearest vessel is a carrier of plague victims destined for the infamous Terminus, the time-bomb planet ticking at the centre of the universe...