The Doctor (William Hartnell) and his companions land on a spaceship orbiting a distant and mysterious world, where a human crew lie frozen somewhere between life and death. The planet is the Sense-Sphere, home of the Sensorites, beings of immense intelligence and power. Unable to leave, the Doctor and his companions must deduce the Sensorites' intentions: are they friendly, hostile, or frightened? And what is the deadly secret at the heart of the Sense-Sphere? This story was originally broadcast on BBC1 between 20th June - 1st August 1964.