The novel “Timewyrm: Exodus” by Terrance Dicks was published for the first time in 1991. It’s No. 2 in the “New Adventures” range by Virgin Publishing.

The Seventh Doctor attempts to pinpoint the time period when the entity known as Timewyrm arrived, but it is difficult to obtain a precise result. The TARDIS transports the Doctor and Ace to 1951, to the Festival of Britain in London. The travelers soon realize they have ended up in a London ruled by the Nazis.

The comments Doctor and Ace exchange are overheard by someone who alerts the local authorities, and the two are arrested. They manage to escape, but the TARDIS is no longer where they left it. To understand when history was altered to help Germany win World War II, the Doctor finds himself in the awkward position of collaborating with the Nazis.