"A Spy on the Home Front" by Alison Hart

My kids love the American Girl books, just like I did as a kid.  I've bought them a lot of the tie-in mysteries over the years, mostly at the second-hand bookstore, but I've never read any of them myself, until now.
A Spy on the Home Front is a fast read with a pretty serious topic: anti-American spying during WWII.  Molly McIntire spends every summer with her grandparents, and she's good friends with Anna Schulz, a girl her age who lives on a nearby farm.  Anna's parents immigrated to America be...