The assassin's curse : A blackthorn key adventure
(Book)

Wherever Christopher Rowe goes, adventure-and murder-follows. Even a chance to meet King Charles ends in a brush with an assassin. All that's recovered from the killer is a coded message with an ominous sign-off: more attempts are coming. So when Christopher's code-breaking discovers the attack's true target, he and his friends are ordered to Paris to investigate a centuries-old curse on the French throne. And when they learn an ancient treasure is promised to any assassin who succeeds, they realize the entire royal family is at stake-as well as their own lives. -- from Amazon.