An early serial from the long-running BBC television series starring William Hartnell as the original Doctor Who. When the Doctor and his fellow travellers on the TARDIS board a moving spaceship they are surprised to discover that its occupants appear to be dead. Ian Chesterton (William Russell) finally manages to revive a few of the crew and discovers that they have been banned from leaving the orbit of the nearest planet, Sense-Sphere. A number of Sensorites, the race that inhabits the planet, subsequently arrive on the ship and threaten the Doctor and his comrades in a similar manner. A battle of wits ensues in which the humans, aided by the Doctor, attempt to escape the clutches of their alien captors.