(The DOCTOR walks, pondering, over to the Keller machine.) DOCTOR: (To JO.) Err...observers from UNIT. Look at the dial. STANGMOOR PRISON. STANGMOOR PRISON. Today's the first ever world peace conference.
Plan: A: Stangmoor Prison; Q: Where do the Doctor and Jo go to investigate the Keller Machine? A: the Keller Machine; Q: What is the name of the machine that drains evil impulses from prisoners' minds? A: UNIT; Q: Who is handling security at the first world peace conference? Summary: The Doctor and Jo head to Stangmoor Prison to investigate the Keller Machine, which drains the evil impulses from prisoners' minds, while UNIT are handling security at the first world peace conference.