This is a novelization of the fifth serial of the ninth season of Doctor Who, which starred The Doctor in his third incarnation, his companion Jo Grant, and their UNIT comrades, Sergeant Benton, Captain Mike Yates, and, of course, Brigadier Lethbridge-Stewart. The show was first aired in May and June of 1972. The script was written by Robert Sloman, and the novel was written by Terrance Dicks, the premiere adapter of the series. The story features The Master, the Doctor's Moriarty, who has assumed the disguise of a physicist at a research center near Cambridge in order to conduct matter transmission and time experiments. It's one of the more complexly plotted stories, as the best of the back-and-forth time conflict episodes usually are. He is summoning Kronos, a chronovore who feeds on time, and the high priest of Atlantis is transported to the facility, where The Master uses him to summon the monster. The Master then travels back in time to Atlantis and The Doctor and Jo follow him, and a strange battle of the TARDISes (is that the correct plural form?) ensues, after which Jo saves The Doctor, and he soon returns the favor, saving her from the Minotaur in Atlantis. Meanwhile, much disruption of the time streams has occurred... An enraged Kronos is called back to Atlantis, which he destroys, and after another battle The Doctor and Jo emerge victorious and return to the present, but The Master, of course, escapes. It's a fun story, quite plainly- and well-written, and Dicks makes it easy to picture the action and creatures. It's interesting that no explanation is offered as to the seeming contradictions to earlier stories; it's the third or fourth time that the disappearance of Atlantis was addressed in the series, and each explanation was different.