"We must face the facts - the Daleks are closing in on us."

...and they are closing in on the Doctor in a chase through both the universe and through time itself. For having created their own time machine, the Daleks are able to pursue the TARDIS from the planet of Aridius, on to the Empire State Building in 1966, on to the Marie Celeste in 1872 and even on into a haunted house within someone's nightmare.

Recognizing that he must force a resolution to this desperate chase through time, the scene is set for a confrontation between the Time Lord and his most feared enemy on the jungle planet of Mechanus.