Al and Owen return to the Dragon Blood Islands to find clues to the sabre's magical words and find out more about their ancestors amongst the pirates. But when the boys run into Slitgut, who forces them to walk the plank, they get sucked into the infamous Dead Man's Whirlpool and uncover more than they could have expected in their wildest dreams. Will they be able to escape the underwater cave? And will they be able to decipher the cryptic code in the ancient letter they uncover by chance?