first birthday guest to arrive. . . . There's a knock on the door, and now there are two! Now three! Now four! The guests keep arriving until fifty partying monsters wreak havoc and Monster Mom decides that enough is enough. The partygoers reluctantly depart until just that one little monster remains--after the best birthday party ever. Little ones can learn counting and basic math concepts while they're laughing over the rollicking rhymes and hilarious, energetic illustrations.