The Doctor and Amy Pond arrive on the Gemstone Moon of Regol Genaralon where they find a prefabricated human research base that appears to have been abandoned for the last two weeks. At the heart of the research is a Grey Hole (something between a black hole that sucks everything in and a white hole that throws all sorts of stuff out). Grey holes shouldn't exist but, the Doctor explains, "on rare occasions they can break through the boundaries between dimensions." Taking the TARDIS on a journey into the Grey Hole to rescue the research scientists, they travel through the different levels of space-time distortion beyond the event horizon, where light is unable to pass. Homing in on the echoes of the human scientists' brainwaves, the Doctor and Amy find themselves on the edge of oblivion, a