One, two, three. Three tears. Three girls. Three wishes. Three debts left to be paid.



Sélie Bell is perfectly content. Both of her sisters are back home; Corliss is getting married, and Aven is becoming more like herself every day. Plus, Sélie gets to spend nearly every day with her best friend, Pearl, working at the Bells' Apothecaire.



But when a letter arrives for Sélie asking her to bring Pearl home to the nearby island of Salille, Sélie reluctantly agrees to accompany her friend on the voyage. And when they arrive, Sélie is shocked to find out that Pearl is actually Marguerite—Salille's runaway princess.



Before she has the chance to process this news, Sélie finds herself face to face with a mermaid who claims that Sélie must repay her late mother's debt to the sea witch. Sélie secretly begins completing a series of tasks before the painful new scales growing on her legs overcome her and she turns into a mermaid, losing not just her life on land but any chance she had at love with a certain beloved princess.