When the TARDIS lands in a quarry on Earth, Sarah unearths what appears to be a fossilised hand, buried in one-hundred-fifty-million-year-old strata. Analysis shows the hand to be silicon-based and inert, but when Sarah begins to act as if possessed, the Doctor suspects that it may still be alive...
The Doctor returns to Peladon fifty years after his last visit, to find Queen Thalira, daughter of the late King Peladon, on the throne. A tense labour dispute between Pel nobility and miners is worsened when apparitions of their deity Aggedor attack and kill several miners. The Galactic Federation desperately needs trisilicate for its war against Galaxy 5 and sends in brutal Ice Warrior troopers to ensure production. The Doctor discovers a devious plot at the heart of Aggedor's appearances.
Time itself is in peril! The Time Lords and UNIT find themselves besieged by a mythic figure from the Time Lords' past hell-bent on destruction. The only way to defeat him is to break the First Law of Time and let the Doctor help himself — literally...
