Between the Sea and Sky by Jaclyn Dolamore
For as long as Esmerine can remember, she has longed to join her older sister, Dosinia, as a siren–the highest calling a mermaid can have. When Dosinia runs away to the mainland, Esmerine is sent to retrieve her. Using magic to transform her tail into legs, she makes her way unsteadily to the capital city. There she comes upon a friend she hasn’t seen since childhood–a dashing young man named Alandare, who belongs to a winged race of people. As Esmerine and Alandare band together to search for Dosinia, they rekindle a friendship . . . and ignite the emotions for a love so great, it cannot be bound by sea, land, or air.