Sissel Eklund is a product of a genetic engineering program created by a group known as the Adigeons. She has an off-the-charts IQ, the strength of three men, and is immune to illnesses due to a hyper-augmented immune system. In their quest to create a race of super assassins, the Adigeons used chess to develop Sissel's ability to see situational variations and adjust in such a way that she always came out a winner. At the age of nine she was routinely defeating grandmasters. Sissel used to have a command implanted in her brain that allowed the Adigeons to control her. However, due to a motorcycle accident and a severe concussion, that system was severed. Now, she runs a Chicago bakery, serving the best liquor-filled cream puffs in the city. But when Antonio Reyes, an arrogant Argentine chess grandmaster and owner of Bodega Reyes, a producer of highly rated wines visits Chicago for a chess exhibition, Sissel can't resist entering. Much to Reyes surprise, Sissel beats him in nine moves. In a follow-up game, it only takes her fifteen moves to defeat him, leaving him infuriated.About the time that Sissel is beating Reyes, her friend Detective Harry Sanchez, a ten-year veteran of the Chicago police force's narcotics division, is investigating the appearance of a new supplier of ultrapure cocaine and methamphetamine to the city's gangs. A reporter investigating the new supplier is found dead in her bathtub, shot through her mouth and both eyes. Her wounds are the signature of a shadowy assassin known as the Peuchen, who has been loosely associated with a mystery man called El Mago or the Wizard. Harry plays a frustrating game of real-life chess as more bodies fall at the hands of the Peuchen. But when he stumbles onto El Mago's identity, the unthinkable happens to his family. As Harry and Sissel's chess games converge, it poses the biggest challenge Sissel has ever faced and there is only one way it can end-Checkmate.