The Eleventh Doctor takes Amy Pond and Rory Williams to a recording of The Goon Show in London 1959 to Rory's delight. Atop a double-decker bus, they find frightened and alarmed passengers. The Doctor leads them up to a "third" deck. Whichever way they go they end up in the same place. Through a window the Doctor sees a giant eye. He realises the bus is actually a shapeshifter. They are creatures which hide on developed worlds. They take on unassuming shapes, lure creatures inside and consume them. The Doctor explains the shapeshifter often takes on qualities it doesn't want.