It's Splat's first day of school, and he's worried. He tries every excuse he can think of to get out of going, but his mother dismisses every one. For moral support, Splat hides his best friend, Seymour, a mouse, in his lunchbox.

The day doesn't seem to go so badly, until Splat learns that cats chase mice. Splat doesn't chase mice! At lunchtime, Splat opens his lunchbox, Seymour pops out, and chaos ensues when Splat's classmates do what cats do. But when the door to the milk cupboard gets stuck and milk time is canceled, Seymour opens the door, saves milk time, and changes the cats' minds about chasing mice!

A New York Times bestseller and TIME magazine's number four picture book of 2008, this charmingly illustrated story will help young children overcome their own worries with humor and encouragement.