While he's at Nan's, Jasper John Dooley discovers his dad's beloved old Marcel Mouse toy. Orange and plastic with big ears and big feet, the toy was based on a character in a television show from when his dad was small. Jasper loves Marcel so much he slides him onto a long string and wears him around his neck! However, just like the TV show's theme song that Jasper's dad teaches him says "Marcel Mouse! Marcel Mouse! A mouse who's lots of fun! Marcel Mouse! Marcel Mouse! He's a tricky one!" Hanging on to Marcel proves to be tricky, indeed. It's no big deal when Marcel goes missing for a short time in Jasper's bedroom, and then later in the principal's office at school. But then something truly and unimaginably terrible happens to Marcel. And Jasper may have lost him forever!