How do you foist responsibility on a good-for-nothing socialite? With a chance handshake, of course. This particular handshake results in our heroine contracting something more disturbing than cooties.
On Ciress magic is a very real and ubiquitous element. Society is structured around it. Everything, in fact, is run by the seven magical guilds. All her life the gifted and no-nonsense Genevieve Villard had strived and studied, determined to become a Guild Master, and at last she's on the cusp of achieving her goal. But then, during her Rite of Ascension, the mystical ritual which officially elevates her to Master of the Nouveau Guild, the fickle universe gives her a wink.
In the audience at Genevieve's ceremony is her capricious younger sister, Giselle, and Giselle couldn't care less about magic. She'd rather keep an eye out for the next party. Imagine her distress when a passing handshake from a stranger result in a mark on her right palm, and this mark suddenly activates and disrupts Genevieve's Rite of Ascension. Suddenly the spirit of the Nouveau Guild's founder - meant to pass into Genevieve to act as guide and repository of all arcane knowledge contained in her guild - instead is sucked into Giselle. But it doesn't end there. Giselle's mark also yanks the founding spirits of the other six guilds from their hosts and then plants them within the party girl. Oh, she doesn't like this. Just like that, though disinclined and wholly untrained, Giselle had become the most powerful sorceress maybe ever in the history of Ciress. Her older sister is pretty cheesed.
The mark on Giselle's palm, that sigil, apparently creates a "synthesis of all the major magic." Meaning that she might know squat about magic, but she can still wield the damn thing, and effectively. But it doesn't help that most of the spirits trapped within her rail against their captivity. Their original hosts want the spirits back in the worse way, and since these hosts are pretty formidable magic users themselves, they quickly make things tough and dangerous for Giselle.
Also aggravating Giselle is an odd feline-like pet (called a squit) that came out of nowhere and began speaking to her. Giselle decides to call it Skitter (although it prefers the name "Dirk").