Ty is a 15 year old boy who was born Subsea, and has been living there his entire life. Because of this, Ty has gained the ability of a Dark Gift. In this case, his power allows him to use echolocation, allowing him to see with sound, even with his eyes closed.
Ty, being able to use echolocation, can communicate with dolphins and whales. It isn't necessarily talking or having a conversation, but he's able to call for help or give out warnings.
Ty has met a Topsider, a girl named Gemma, whom he ends up loving. Towards the end of the book, Gemma almost dies, but is saved by Ty when he does CPR on her. They end up living together since she has no where else to go, because her brother Shade/Richard signs a form that allows her to be free and not in the hands of her old boarding school.