Vicious deep trilogy

When Tristan Hart is washed out to sea, he resurfaces on Coney Island three days later with no memory of what happened. Gradually, Tristan pieces together his lost memory and learns he is heir to an undersea kingdom and has become a tool caught up in a war between powerful forces of the oceans.

As Kurt and Tristan battle for the Sea King's throne, sea witch Nieve kidnaps Layla and raises an army of mutant sea crature to overthrow the crown.