Deep Water by Emma Bamford

Newly married, Virginie and Jake decide to buy a boat and sail the Indian Ocean. When someone tells them about an uninhabited island called Amarante, they decide to go there. It turns out that others have also made it their temporary home—an Aussie named Roly (and his dog, Gus) and a Canadian couple, Stella and Pete. Right after Virginie and Jake arrive, wealthy Vitor and his girlfriend Teresa show up. Virginie and Jake had briefly met Vitor and Teresa on the mainland. Things are going fine at first, but the reader knows that soon the situation will somehow turn violent, leaving Virginie and Jake fighting for their lives--thanks to a first chapter that has the duo being rescued by the Royal Malaysian Navy and a traumatized Virginie saying "It's all my fault. I killed them." What really happened on Amarante? A beach read that's hard to put down.