Isabelle and Jean-Claude undertake an airship expedition to recover a fabled treasure and claim a hitherto undiscovered craton for l'Empire Celeste. But Isabelle, resulting from a previous attack that tried to subsume her body and soul, suffers from increasingly disturbing and disruptive hallucinations. Disasters are compounded when the ship is sabotaged by an enemy agent, and Jean-Claude is separated from the expedition. In a race against time, Isabelle must figure out how to ward off her ailment before it destroys her and reunite with Jean-Claude to seek the fabled treasure as ancient secrets and a royal conspiracy threaten to undo the entire realm.

Isabelle des Zephyrs has always been underestimated throughout her life, but after discovering the well of hidden magic within her, unveiling a centuries-long conspiracy, and stopping a war between rival nations, she has gained a newfound respect amongst the cutthroat court. All that is quickly taken away when Isabelle is unfairly convicted of breaking the treaty she helped write and has her political rank and status taken away. Now bereft, she nevertheless finds herself drawn into a mystery when her faithful musketeer Jean-Claude uncovers a series of gruesome murders by someone calling themselves the Harvest King.

Born with a physical disability, no magical talent and a precocious intellect, Princess Isabelle des Zephyrs has lived her life being underestimated by her family and her kingdom. The only person who appreciates her true self is Jean-Claude, the fatherly musketeer who had guarded her since birth. All shall change, however, when an unlikely marriage proposal is offered, to the second son of a dying king in an empire collapsing into civil war. But the last two women betrothed to this prince were murdered, and a sorcerer-assassin is bent on making Isabelle the third. Step by dangerous step, Isabelle must unravel the lies of her enemies and discovers a truth more perilous than any deception.