Set between Revenge Of The Cybermen and Terror Of The Zygons, the Fourth Doctor and his team of companions are on their way back to Earth when they encounter a Black Sun that catapults them and the TARDIS through space and time into an alternate 21st Century and the whereabouts of Moonbase Alpha ever since Breakaway that occurred on the 13th of September - 1999.
Landing the TARDIS on Moonbase Alpha as set between The Metamorph and The Exiles, Harry Sullivan is able to attempt a treatment that rejuvenates Victor Bergman. Sarah is tempted to leave Earth behind and join the crew of Moonbase Alpha alongside Maya the Psychon. In the meantime, the Doctor must help Commander Koenig and Dr. Russell in saving Alpha from the Scratchman.
