The best night of our lives?

Nani goes on a cruise with her best friends and her boyfriend Julian. They were having the time of theirr lives until... The cruise sinks... Nani and her friends survived, but Julian is missing. Everyone thinks he's dead but she has the feeling that he's out there somewhere... To top it all off her phsycopath younger sister escapes from a highly secured mental hospital she was being held on. She wants to kill them all. Nani isn't completely innocent either. She has a dark past which only her sister knows about. Will this past help her or destroy her? Will Nani find her lover? Will she survive to her sister's attacks?