When the submarine departed, none of the ten people on board knew it would turn into a nightmare. Trapped on the sunken vessel and unable to escape, one of them is discovered dead. The tension escalates as the survivors realise there is a murderer among them, who is preparing to strike again and again… With mounting desperation, people begin to turn on each other. While they struggle to identify who is responsible, each must contend with their own past and the secrets they are hiding. But who is who? And which of them will be next to die?