Series three's Utopia took us further than the Doctor had ever gone as the last remnants of humanity sought to find a last refuge before the end. We discovered of course that the Master enslaved them all - or at least the majority of them as the Toclafane - and brought them back to 21st Century to attack humanity at its most vulnerable. But in Listen the Doctor - and Clara - went even further, to the point where all life was dead and just one man had made it; time traveller Orson Pink. The Doctor was a little disappointed to learn that he wasn't the last man alive, though as we discovered his worst nightmare was still there waiting for him. Or so we thought. The revelation behind what the thing banging on the airlock door and hiding under Rupert's bed was sure to divide fans, but finding the bleak desolation that was the end of the universe was just as terrifying.