When is a mystery not a mystery? When it's a birthday party! Someone seems to have stolen Ken's bike from the front porch, leaving chain and lock attached to the post. Jenny agrees to help solve the mystery of what has become of it, claiming that ""My Dog"" will help, and meanwhile wondering why no one remembers to wish her a happy birthday. The other kids claim that My Dog isn't bright enough to help; she's bright enough to follow a popcorn trail, but it's the bike track through spilled talcum powder leading to Ellen's house that takes Jenny to her surprise birthday party. Like others in this gentle mystery series, this is pleasant but not exceptional; however, it is satisfactory enough as a new easy reader in a lean season, helped substantially by Gackenbach's sturdy, expressive kids and ebullient dog.