RESPONDING TO A DISTRESS CALL, THE TARDIS materialises in the hold of the Fancy, a pirate ship under the command of Captain Avery. The Doctor, Amy Pond and Rory Williams are taken for stowaways and the Doctor is forced to walk the plank, but when Amy brandishes a cutlass the travellers are surprised to find the pirates are terrified of acquiring even the slightest injury.
Rory and a pirate named Dancer both receive minor cuts, but a black spot inexplicably appears in each man’s palm and they are targeted by the
Siren, an ethereal mermaid who emerges from the sea to intoxicate her victims with her song. Dancer disintegrates in a cloud of dust and Avery explains that the Siren has been hunting his crew ever since the ship was becalmed eight days earlier. To prevent Rory suffering the same fate they all retreat into the hold, but the Siren uses the bilge water there as a portal to take another pirate, De Florres, after he is bitten by a leech.
“Yo ho ho! Or does nobody actually say that?” The Doctor
Barricading themselves in the ship’s armoury, they discover the Captain’s son, Toby, hiding in a barrel. A stowaway since the ship left port, Toby has contracted typhoid fever and has also been marked with a black spot: the Siren is selecting both sick and injured. Then the Doctor suddenly realises that any reflective surface provides her with a portal, including the polished metal of the pirates’ treasure.
During a storm, the Siren comes for Toby and Rory is knocked overboard by a loose boom. Unable to save his friend from drowning, the Doctor enables the Siren to take Rory too, in the hope that he has correctly surmised that she is not actually killing her victims but teleporting them to another plane. Now the only way to rescue Rory and Toby is for the Doctor, Amy and Avery to let the Siren target them as well…