Scream

You board a cruise ship, and you hear a cry of severe pain and distress. The intercom crackles to life, with the Captains voice, "Passangers, I'm sorry to inform you if this, but there has been a mass murder. Go to your rooms and lock the doors, and we will hunt down this vile beast." A few hours of pacing your room wondering who did this, is suddenly interrupted by the intercom once again. "One victim down, 6183 left. Good luck!" Your door swings open.