Valentine Marsh has had a gut-wrenching year. While negotiating the usual rocky social terrain of high school, she's had a magical heritage thrust upon her, defeated a monster at grim personal cost (The Bronze King), and by a hair's breadth foiled the soul-stealing scheme of a pair of evil necromancers (The Silver Glove). And even now she can't catch a break!

During a New Year's Eve party in New York, Valentine and her friends unwittingly launch a far-reaching magical flare. Within days, the sending attracts a new threat—an arrogant young noblewoman masquerading as a foreign student named "Bosanka Lonatz." Bosanka gives Val a deadline to reconvene the New Year's party, aka the "Comet Committee," to help her summon her own lost people who might very well take over Earth, in place of the alien world they once ruled but had to abandon. With Granny Gran lying comatose in the hospital, Val must race time once more to forestall otherworldly disaster—but first she's got to rally her scattered, unpredictable friends and get a grip on her own fears, for a final confrontation with an angry and powerful enemy.