During the Nazis' monthly Sunday dinner at the Thibaut farm on November 28, Paul takes Maddie away to another house to practice shooting guns and wiring explosives. This gets her out of the Nazis' way, since she's a suspicious character.
Maddie—as Käthe—is now doing some intelligence work. Because Engel won't recognize her and she'll be gone in a few weeks (she hopes), it's her job to deliver a message about the Resistance to Engel.
In order for Maddie to get a good look at Engel, as she's never seen her before, Paul and Maddie come back around the time Engel has to get out of the Nazis' Mercedes to open the farm gate. The Gestapo travels in style.
Paul helps Engel, making such a show of groping her while he's at it that nobody notices Maddie.
Maddie observes that Engel is about her age and would be good-looking under the right circumstances.
She also notices that the German captain looks haggard. She thinks it's probably due to the fact that he's in trouble with Nikolaus Ferber, his superior officer, over the Georgia Penn interview and over the fact that a set of keys went missing in the Gestapo last week.