It is the mid 1970's and the U.N.I.T annual Christmas party is in full swing. Corporals Maisie Hawk and Carol Bell are coming to the end of their shift when an unidentified craft appears on their radar. The Doctor, Sarah Jane Smith and the Brigadier all rush to the crash site where the Doctors worst fears are met when he realises that the unidentified craft is in fact a TARDIS escape pod containing The Master....