In the third episode of the four-part story "Snakedance," the Doctor (Peter Davison) has arrived on the planet Manussa, there to prevent the malevolent mind-force Mara from using a local celebration to regain its full powers. Unfortunately, the Mara has already mentally enslaved the Doctor's companion, Tegan (Janet Fielding), who has managed to steal the Great Crystal, an artifact crucial to the Mara's ultimate victory. Written by Christopher Bailey, "Snakedance, Episode 3" first aired on January 25 1983. ~ Hal Erickson, Rovi