Parts: 6
Writer: Peter R Newman
Airdates: 20 June 1964 - 1 August 1964
Production Code: G

Episode Titles: Strangers in Space; The Unwilling Warriors; Hidden Danger; A Race Against Death; Kidnap; A Desperate Venture

Doctor: first
Companions: Susan, Ian, Barbara

Creature Feature: Sensorites

Story: The TARDIS lands on a spaceship in the twenty-eighth century, but to the shock of the TARDIS crew, its two officers both appear to be dead at the controls. Fortunately, both are still alive and able to be revived. Upon recovering, Captain Maitland and his fellow officer, Carol Richmond, inform the TARDIS crew that their ship has been trapped in orbit around a nearby planet, the Sensesphere. The beings who live there, known as Sensorites, were responsible for their comatose state. Maitland suggests that they leave, but they find that departure is impossible, for the TARDIS lock has been removed and the Doctor cannot get in.

When Barbara and Susan go to fetch water, they encounter the ship's other crew member, John. Having previously met the Sensorites, John has become almost insane. Meanwhile, two Sensorites make their way onto the ship, and Barbara and Susan realize that the Sensorites are controlling John's mind. With Maitland's help, they escape from the Sensorites. The Doctor discovers that John has learned one of the Sensorites' secrets, and the creatures are desperate for it not to get out. When he learns that the planet contains large deposits of molybdenum, a valuable mineral, the Sensorites decide to confide in him.

But not all of the Sensorites agree with this decision. The City Administrator decides to take matters into his own hands, and plots the destruction of the TARDIS crew. Then Ian is poisoned when he drinks some of the local water. With Ian rapidly dying, and the others in danger of sharing his fate, can the Doctor solve the Sensorites' problems in time for them to leave alive?