Book Two of Beneath The Waves.
Oliver had been a marine researcher for several years before going back through school to add aquatic doctor to his resume. He had a short fuse when it came to his temper but he was always loyal to Parker and Jayson, his two best friends, and took his job very seriously. His life happily revolved around the ocean and the amazing creatures that swam beneath its waves until an unfortunate accident leaves him questioning his ability to ever return to the thing he had once loved with all his heart.
When Eko is kidnapped from his home in the deep Atlantic by members of an ancient cult, his only hope of returning to his life as a merman is the Heart of Poseidon, the source of his people's power, and the object the cultists want most.
Following a grueling transformation into human form, Eko finds himself trapped in the small but dangerous town of Porthaven, Maine where he desperately searches for a way home. But the closer he gets to his goal, the more he finds himself drawn to his human savior, a kind human girl who helps him see the Upperworld and his new air-breathing body not as a prison, but as an opportunity for reinvention after the iron caste system of his old life. But even she is wrenched away when the cult leader discovers Eko's whereabouts and threatens everyone standing between him and the Heart of Poseidon. Forced to tap into a dark and lethal power in order to save the girl he's come to love, Eko uncovers ancient truths, and begins to suspect that the cult has motives poised to change both worlds forever. With consequences far worse than anyone could imagine.