Simon Thorn and the Shark's Cave (Paperback) by Aimee Carter

Simon Thorn has only recently discovered that he's an Animalgam--a member of a secret race of people who can shift into animals. Now, after years of being bullied, he has found a home where he truly belongs, at a secret Animalgam academy.

But danger lurks around the corner . . . Simon's evil grandfather, Orion, is bent on taking over the entire animal kingdom. He intends to gather the pieces of a terrible weapon that could shred the very foundations of their world. That is, unless Simon can find the pieces first.

So when Simon's dolphin Animalgam friend Jam is summoned home to the underwater kingdom's headquarters, Simon sees an opportunity to secure another piece. But as soon as he and his friends arrive, their search is complicated by Jam's strict family--and a potential traitor among their ranks. Can Simon locate the piece before the entire underwater kingdom is put at risk?

With plenty of action and adventure and characters full of heart, the Simon Thorn series is perfect for fans of Rick Riordan and Brandon Mull.