Emily Windsnap and the Castle in the Mist (Emily Windsnap, #3)

A fin-tastic follow-up to "The Tail of Emily Windsnap" and "Emily Windsnap and the Monster from the Deep"
Ever since I discovered I was part mermaid, nothing in my life has been simple. So when I spotted the gigantic diamond ring on the seabed, I should have turned on my tail and swum away. I most definitely shouldn't have put it on.
But how was I supposed to know that the ring was one half of the key to unlocking an ancient curse-a curse put in place by Neptune himself? And now Neptune has put a curse on me, too: in a few days, I'll no longer be half-human and half-mermaid, and I'll have to say good-bye forever to one of my parents. Unless, with the help of a mysterious boy named Aaron, I can find the missing ring and break all of the curses at once. . . .