Mirabell's life revolves around middle school, her best friend Stu, and fencing, a sport that her grandmother taught her.

But she soon discovers that she is the direct descendant of Black Sam Bellamy, a pirate cursed with immortality, and that she must help him find his own long-lost treasure to save her abducted grandmother.

As Mirabell and her friends race around Cape Cod, looking for clues, Bellamy's evil nemesis pursues them, convinced that they have the treasure and the key to opening a portal to the pirate ship, Whydah.

Will Mirabell learn to trust those around her and save her grandmother before he catches up to them and opens the gateway to the pirate world?