The Hand of Fear is a classic slice of Doctor Who from the show's so-called 'Golden era'. Tom Baker is at his best; alternately whimsical and filled with supressed rage at the injustice he sees. The story is also particularly noteworthy for being the swansong of Elisabeth Sladen as feisty journo Sarah-Jane Smith.
The Doctor and Sarah find themselves in a quarry in timeless 'Who' tradition; Sarah is subsequently buried as an explosion rips through the rocks. When he unearths her, The Doctor finds she is clutching a fossilised hand; this leads the time-travellers to the planet Kastria where they encounter the reborn Eldrad, a monstrous dictator put to death by his own people...
What makes this serial so special is the chemistry between The Doctor and his 'best friend'. There is real pathos in their parting and her hideous Andy-Pandy outfit aside, Sarah is fantastic. The other plus is the set design, particularly the planet Kastria and the manipulative Eldrad, all booming voice and figure-hugging shimmery lycra.
If you only ever watch one 'classic' Doctor Who story then make it this one!