Third grader Ben meets a "Bird Girl." She's a crow most of the time and at others a girl. She invites Ben to join the Bird Club to assist in a mission to cross The Impossible Divide, a place that separates people from animals. In Book One of this seven-book serial, Ben joins the Bird Club just as its oldest member, a fifth grader, prepares to quit it. Ursula doesn't want to leave the club, but she'll soon turn ten. And the Bird Girl (who calls herself Benita) becomes invisible to anyone over ten. Ursula, Benita, and the club members prepare for this sad occasion with a special club meeting. An unseen stranger also attends, one who is about to change everything they know.