Marvin is a beetle living with his family in the wall of a cupboard under a kitchen sink. They share space with the human family, the Pompadays, who occupy the apartment in which the cupboard resides. The cupboard provides everything Marvin’s family needs: food from the garbage can, soft walls for carving out their home, and dripping water.

Marvin is awoken one morning by the frantic pacing of Mrs. Pompaday. His mother retrieves him from his cotton ball bed, telling him there’s an emergency. Marvin’s family—Mama, Papa, Uncle Albert, and Cousin Elaine—have been having a tense discussion in the next room. Elaine informs Marvin that Mrs. Pompaday has dropped her contact lens down the drain of the bathroom sink. Marvin’s aunt, uncle, and cousin live in the bathroom cupboard; Marvin’s family doesn’t want to risk having Mrs. Pompaday call a plumber because the plumber might spot the worn away cupboard walls. Marvin is the only one in his family who can swim; his family recruits him to retrieve Mrs. Pompaday’s contact lens. Marvin’s parents are proud of the fact that he can swim but are also concerned about Marvin’s safety.

Marvin has been practicing swimming in the cap of a juice bottle, but he is nervous about swimming down a drain.