For once, everything in twelve-year-old Josephine's life is going according to plan. She's finally proved that girls belong on the cricket team and earned a spot as a starting player! And she's confident that she and her best friend, Ahkai, will both be accepted to their dream secondary school. Nothing can stop Jo now -- not even the memory of the vengeful sea spirit she vanquished last year.

But then a series of disasters strike. Ahkai suddenly seems to have a new best friend -- the annoyingly perfect Lynne. Then Jo isn't accepted to the same school as Ahkai! Even worse, Jo keeps having eerie encounters with a mysterious figure lurking in the shadows -- a figure who bears an unsettling resemblance to the fearsome Heartman rumored to steal children's hearts...

Jo doesn't know where to turn. With Daddy away, the only person who'll believe her is Ahkai, but Jo is too proud to ask for help after being replaced. By the time she musters the courage to approach him, it's too late.

Ahkai has disappeared without a trace.

He's been taken by the Heartman.

None of the adults believe Jo. The Heartman is just a legend, after all. But Jo knows that the fearsome creature is real and that if she doesn't find his lair soon, Ahkai will be lost forever.