The Doctor, Ian, Barbara and Susan arrive in the TARDIS on board a spaceship. Their initial concern is for the ship's human crew, who are suffering from telepathic interference from the Sensorites, but Susan communicates with the Sensorites and finds the aliens fear an attack by the humans and are just defending themselves. Travelling to the Sense Sphere (the Sensorites' planet) the Doctor seeks to cure an illness to which the Sensorites and Ian have succumbed, but finds it has been caused by deliberate poisoning. The political manoeuvring of the Sensorite City Administrator poses another threat to the TARDIS crew as he seeks to discredit and implicate them.
as The Doctor
as Susan Foreman
as Barbara Wright
as Ian Chesterton
as John
as Carol
as Maitland
as Commander
as First Human
as Second Human
as First Sensorite / First Scientist
as Second Sensorite / Second Scientist / Warrior
as Third Sensorite / City Administrator
as Fourth Sensorite
as First Elder
as Second Elder
as Sensorite
as Sensorite
