Arriving at the Shackleton Crater on the Moon in 2039, two Earth astronauts in search of water find the Eleventh Doctor and Amy Pond already there. The crater, always on the dark side of the moon has been probed to reveal a good source of ice. A torch is shone into the crater. There is no reflection of light from any ice, but the torches pick out something else in the dark, something that races out towards them.