Cortes - Useless against Davy Jones

Gripping his sword, Jack backed away from the terrifying figures. "One more thing, Jack Sparrow," Morveren said. "That sword in your hands is powerless against creatures who reside in Davy Jones's locker--including your opponents."

The three Blue-tails smiled, then addressed Jack in unison. "Good luck, Jack Sparrow."

***

The Sword of Cortes, Chapter 6