(He points to a peg by the door with a fur coat on it.) (One of the spars of the bridge falls forward and for a moment nobody moves. (SUSAN calls from by the entrance to the passageway.) HUT
(VASOR is sitting at his table, smiling as he looks over the travel dials and the necklace of keys. IAN hands the other keys to SABETHA.) IAN: (Taking them.) IAN: And four dead warriors ... to guard it, eh? Mind the slope. SABETHA: In these clothes? Take your hands of her! The SOLDIER falls into the chasm, screaming, as IAN stares on, grimly. They can't have been gone long.
Plan: A: The TARDIS; Q: What ship arrives on the planet Marinus? A: the planet Marinus; Q: Where does the TARDIS arrive on an island of glass surrounded by a sea of acid? A: The travellers; Q: Who is forced by the elderly Arbitan to retrieve four of the five operating keys to a machine called the Conscience of Marinus? A: the keeper; Q: What is Arbitan's role in the Conscience of Marinus? A: their own sinister purposes; Q: What do the evil Yartek and his Voord warriors plan to use the Conscience of Marinus for? Summary: The TARDIS arrives on the planet Marinus on an island of glass surrounded by a sea of acid. The travellers are forced by the elderly Arbitan to retrieve four of the five operating keys to a machine called the Conscience of Marinus, of which he is the keeper. These have been hidden in different locations around the planet to prevent them falling into the hands of the evil Yartek and his Voord warriors, who plan to seize the machine and use its originally benevolent mind-influencing power for their own sinister purposes.