This whimsical look at the friendship between a young female narrator and a fast-growing sea serpent will amuse young listeners while providing adult readers with the bittersweet opportunity to ponder the ways relationships grow and change. Smaller than the girl’s arm, the sea serpent shows up unexpectedly one day in the bath. He quickly outgrows his tank, then the tub, all the while talking longingly of the sea “where manta rays swim like dancing blankets and there are…fish shaped like guitars.” So the two go down to the seaside, where they romp and play. Although she’s loath to give him up, she knows he’ll be happiest in the sea, so she encourages him to strike out on his own. Slater’s lyrical text is accompanied by Chien’s delightfully watery paintings in blues and greens, filled with squiggles, bubbles and a childlike charm; shifts in perspective give readers and narrator alike a real sense of the serpent’s ultimate immensity. Imaginative and engaging. (Picture book. 4-7)