for Mousetraps by Pat Schmatz
Back in grade school, Maxie and Rick were best friends. Rick would design crazy inventions, and Maxie, the artistic one, would draw them. Then something terrible happened to Rick, and he vanished from her school and her life. Years later, he shows up at Maxie's high school. In some ways he's the same person she once knew. But in other ways - frightening ones - he's very, very different . . .
Publisher description retrieved from Google Books.