Release Message:  On the planet Marinus, the Doctor (William Hartnell) and his companions are enlisted by Arbitan to seek out the keys to an ancient and powerful machine.

Description:  On the planet Marinus, the Doctor and his companions are enlisted by Arbitan to seek out the keys to an ancient and powerful machine. Their quest takes them across time and space; will they be able to return the keys before Marinus falls under the control of the alien Voord?