The Doctor, Amy and Rory, board a pirate ship lost at sea, there's a bit of a kafuffle after the sight of blood summons something like a banshee (but with a better song), this is usually preceded by the mark of the Black Sharpie, also causes everyone to flee, though not that far as they're on a boat lost at sea. Then the mark gets Rory, and before too long they are down to three, the Doctor, the Captain and Amy and then it gets all science fictiony, and a bit silly, but it goes with the territory. The next episode's a treasure though you'll see, might be the best one ever.