Lucy, Wyatt, and Rufus follow Flynn to Nazi Germany to protect the timeline from whatever he's planning to do. They suspect it involves the nuclear bomb that he stole, but really, it's about a scientist that is supposed to be captured by the Allies from Hitler's control.
Flynn's plan is to give the scientist who helped get the United States to the moon, helped win the Cold War, and basically developed rocket science to the Soviet Union, so Russia will be the winner of the war and the first to get someone to the moon. All in his war with Rittenhouse.
The plan, as usual, doesn't work out, so Ian Fleming, the man who is helped the trio and later writes James Bond, is outed as a British spy by Flynn, ruining his cover, but not ruining his future literary works, and in turn, films.
Also, as usual, Wyatt wants to kill the person they're supposed to protect and change history, as does Ian, but Lucy defends this man solely due to his contributions to history and science in his life, and the men listen to her. It's always up to Lucy to be the voice of reason and save the day.