Synopsis: After a failed attempt to fight off the wasps, the Doctor and Jamie slip into a narrow crevice. They discover that it leads to the remains of an underground city. Thinking they've escaped, they turn around to the angry metallic chant of Quarks waiting for them there in the dark . . .
Notes: How, precisely, the Quarks got into the underground city, when the entrance was said to be tight for Jamie and the Doctor to squeeze through, is a little mystifying. Quarks are notably thick around the middle.