When ex-marine Sarah French joins a luxury superyacht as on-board security, she's excited to get her life - and career - back on track. Surrounded by crystal waters, it seems like the perfect place to start over. As they head into open water, though, tensions between the crew quickly build. And when someone goes missing, Sarah has a terrifying realisation. One of them is a killer. All of them are suspects. To protect the other passengers, Sarah needs to uncover the killer's identity, and return the boat safely to shore. But there's a storm on the horizon - and not all of them will make it out alive...