Antagonist
Character Role Analysis
Hauptsturmführer Amadeus von Linden
The antagonist is the bad guy, the one who is working against the protagonist and keeping her from achieving her goals. Von Linden is the head of the Ormaie Gestapo, and as such, he's working against both our protagonists: he takes Julie prisoner and interrogates her, and he's the figurehead of the specific organization Maddie makes it her mission to destroy.
The first time Julie describes von Linden, she likens him to Captain Hook, while describing herself as Peter Pan. Maddie calls him her "mortal enemy" and asks, "How can my whole being, my whole life up to this point, be matched to one man in deadly combat?" (2.23.98). Identifying an antagonist doesn't get much clearer than that.