Paris, 1809. The Fifth Doctor takes a tour of the Catacombs and meets a sassy Time Agent doing the same... Paris, 1944. The Tenth Doctor misses his target and lands in occupied France. He hides from the Nazis – in the Catacombs. A collision of two Doctors’ timelines triggers a temporal catastrophe, granting the Cybermen dominion over the Earth. The Doctors must travel back in time to find the source of the Cyber-invasion and close the Gates of Hell…