Lottie knows a secret — there’s a shark hiding in the pool where she takes swimming class and that’s why she’s beyond frightened to go in the water. It doesn’t want to eat the other kids — just her. One day, an enormous walrus named Walter emerges from a nearby puddle and follows her home. Lottie confides in Walter about not wanting to go in the water next week even though a pool party is planned. It turns out that Walter, in his quietly funny, slightly loopy, fish finger-eating ways, might just be what Lottie needs to realize that she does indeed have the courage to conquer her biggest fear.