King Neptune has 50 daughters (mermaids), each with a distinctive ability. He likes to boast about them: about Clio’s ability as a gardener, Thetis’s ability as a fish-trainer, Calypso’s singing voice. But Minnow, his youngest, does not know her skill yet – her garden is limp, the fish don’t do what she asks them, she can’t sing.  She is curious, however, and asks lots of questions. One day, a red shoe drops into her path – she is fascinated by it and tries to work out its purpose. Clio, Thetis do not know, and Calypso doesn’t care. "It’s junk. Useless like you." But Minnow is determined to find out. ‘This thing was made with care. It has a purpose and I will discover it!’ She sets out to ask other sea creatures – an octopus, a whale, some crabs. Her journey takes her to the seashore, where she sees a lighthouse, and a little girl coming out of it. To Minnow’s eyes, the girl is half mermaid, and half octopus (with two legs), and on her octopus legs are shoes. The little girl sits at the edge of the sea to play, and one of her shoes comes off. Minnow sees that at the end of her legs are feet – or what Minnow calls ‘leg hands. ’She understands what shoes are for, and excitedly rushes home, where she tells everyone what she has seen and learned.Everyone is pleased, except for Calypso, but King Neptune boasts: "My Minnow is a daring explorer!".

This picture book uses a common fairytale format to show the youngest and smallest of a large family finding her powers, to tell the story of a young mermaid (or siren) who feels overshadowed by her older sisters, but who discovers her own individual talent when her curiosity about a mysterious ‘red shoe’ leads her to explore new parts of the ocean. While the story is not strongly Classical in nature, being influenced by the concept of mermaids established by Hans Christian Andersen, some elements show that Campbell is drawing on his knowledge of myth. The mermaids’ father is King Neptune, the ruler of the deep; Minnow’s oldest sisters have classical names: Thetis, Calypso, and Clio. These first two, Thetis and Calypso, are names of sea nymphs, and their characteristics (caring for sea creatures, singing beautifully) are typical of mermaid lore. Clio, named after the Muse of History, does not have an obvious mermaid precedent, but her name relates to her ‘know-it-all’ nature. The motif of a King with 50 daughters has precedent in Classical myth: e.g. see the daughters of King Thespius of Thespiae in Boeotia, and the daughters of King Danaus of Libya. 

The red shoe, the quest of a mermaid to find out about humans, have links to two Hans Christian Andersen stories: ‘The Red Shoe’, and ‘The Little Mermaid’. Both stories are cautionary tales about the results of excessive curiosity. The motif of feminine curiosity, of course draws from the Pandora myth, but where Pandora releases the ills of the world, The Mermaid and the Shoe, on the other hand, rewards Minnow for her curiosity – she finds out about the world above water and is praised by her father for her daring. Campbell’s exquisite illustrations capture an underwater world full of movement and sinuous shapes, and the story as a whole offers a clever and thoughtful approach.