While riding the subway home from the pool with his abuela one day, Julin notices three women spectacularly dressed up. Their hair billows in brilliant hues, their dresses end in fishtails, and their joy fills the train car. When Julian gets home, daydreaming of the magic he's seen, all he can think about is dressing up just like the ladies in his own fabulous mermaid costume: a butter-yellow curtain for his tail, the fronds of a potted fern for his headdress. But what will Abuela think about the mess he makes -- and even more importantly, what will she think about how Julin sees himself?