The Night Flyers: An American Girl History Mystery

Before Pam's father left to fight in World War I, the two of them trained their pigeons to fly home at night, a time when most birds just want to sleep. This interests a stranger with a foreign accent who comes to town and offers to pay a lot of money for Pam's birds. But when Pam refuses to sell and some of her birds are later stolen, she suspects the stranger may be more than a simple bird enthusiast. He may be an enemy spy!