A pleasantly silly story with a nifty surprise ending: Mimi, a hippo ballerina, and Gustav, a mouse musketeer, fall in love without being able to see each other through the wall that separates them. Trying to get together, Gustav builds an inadequate battering ram while Mimi tries a hot-air balloon that can't take off when she's aboard. Despondent, she leans on the wall, which falls—and neither is disappointed. Howard's lively, decorative illustrations match the text's ebullience. (Picture book. 4-8)