In the conclusion of the four-part story "Enlightenment," the Doctor (Peter Davison) races against the evil Captain Wrack (Lynda Baron) to win a yachting competition in space, the prize of which would prove disastrous should it fall into the wrong hands. The Doctor's old enemy the Black Guardian (Valentine Dyall) attempts to determine the race's outcome, but he eventually faces defeat from an unexpected source. With this episode, Mark Strickson officially becomes a regular in the role of Turlough. Written by Barbara Clegg, "Enlightenment, Episode 4" first aired on March 9, 1983. ~ Hal Erickson, Rovi