It's the best kept secret of a billion dollar industry: Your life is at risk when you go on a cruise. Since 2011, more than 200 cruise line travellers have gone missing and are presumed dead. Many are murdered. While some of the murders have officially been solved, questions still linger. Others remain covered up for nefarious reasons. Cruise Ship Killers shines a light on these cases and aims to uncover the truth of what really happens at sea.