Dateline. scuba divers, shelby, and her husband david, were captivated by the aqua blue waters of a caribbean island, posting a majestic underwater world. but, for one of them, the breathtaking views came at a deadly cost. the tragic twist, that exposes family secrets as dark as they come. here is dennis murphy with the last dive. >> for most of us who enjoy spending time in the water, and the occasional swim, in a backyard pool, it will suffice. it was in total immersion, and an open ocean would do. a ticket to paradise. >> it was incredibly peaceful. it was looking for you, and it was amazin...