UNIT are called into monitor the initial trials of a device called TOMTIT - the Transmission Of Matter Through Interstitial Time - at the Newton Institute at Wootton. Created by the enigmatic Professor Thascales, TOMTIT's demonstration causes unexpected time anomalies. The Doctor soon discovers that TOMTIT is not all that it seems...At the heart of TOMTIT is an ancient crystal, which the Master hopes to use to gain control over Kronos - a Chronovore which feeds on time itself. But the stone he holds is only part of the sacred crystal of Kronos - the main crystal is hidden...The Doctor and the Master journey back in time to the lost city of Atlantis, where the battle for the control of Kronos intensifies... Can the Doctor prevent the Time Monster from being unleashed...?