Doctor Who (1963)

S1E21 The Sea of Death

On the alien planet of Marinus, an era of tranquility has prevailed for many years, thanks to a mind-altering device called the Conscience. However, the Voord, a formidable race, have gained resistance to its influence. As a result, Arbitan, the guardian of the Conscience, is compelled to hide its essential control keys across the landscape. Seeking assistance, he turns to the time travelers to help retrieve them. Their quest will lead them through an extraordinary odyssey, fraught with dangers at every turn...