A blockbuster, near-future science fiction thriller, S.L. Huang's Zero Sum Game introduces a math-genius mercenary who finds herself being manipulated by someone possessing unimaginable power..... Cas Russell is good at math. Scary good. The vector calculus blazing through her head lets her smash through armed men twice her size and dodge every bullet in a gunfight, and she'll take any job for the right price. As far as Cas knows, she’s the only person around with a superpower...until she discovers someone with a power even more dangerous than her own. Someone who can reach directly into people’s minds and twist their brains into Moebius strips. Someone intent on becoming the world’s puppet master. Cas should run, like she usually does, but for once she's involved. There’s only one problem... She doesn’t know which of her thoughts are her own anymore.

Cas Russell is back—and so is her deadly supermath. Cas may be an antisocial mercenary who uses her instant calculating skills to mow down enemies, but she’s trying hard to build up a handful of morals. So when she’s hired by an anguished father to rescue his kid from an evil tech conglomerate, it seems like the perfect job to use for ethics practice. Then she finds her client’s daughter . . . who is a robot. The researchers who own the ’bot will stop at nothing to get it back, but the kid’s just real enough for Cas to want to protect her—even though she knows she’s risking everything for a collection of metal and wires. But when the case blows up in her face, it plunges Cas into the crossfire of a massive, decades-long corporate espionage war. Cas knows logically that she isn’t saving a child. She’s stealing a piece of technology, one expensive and high-stakes enough that spiriting it away is going to get innocent people killed. But she has a distraught father on one hand and a robot programmed to act like a distraught daughter on the other, and she’s never been able to sit by when a kid is in trouble—even a fake one. Screw morals and ethics. All Cas wants to do is save one little girl.

Cas teaches Pilar to shoot. Considering Cas is an acerbic mercenary and Pilar is a delightful admin, this goes about how you'd expect.

Cas Russell has always used her superpowered mathematical skills to dodge snipers or take down enemies. Oh, yeah, and make as much money as possible on whatever unsavory gigs people will hire her for. But then one of her few friends asks a favor: help him track down a stolen math proof. One that, in the wrong hands, could crumble encryption protocols worldwide and utterly collapse global commerce. Cas is immediately ducking car bombs and men with AKs—this is the type of math people are willing to kill for, and the U.S. government wants it as much as the bad guys do. But all that pales compared to what Cas learns from delving into the proof. Because the more she works on the case, the more she realizes something is very, very wrong . . . with her. For the first time, Cas questions her own bizarre mathematical abilities. How far they reach. How they tie into the pieces of herself that are broken—or missing. How the new proof might knit her brain back together . . . while making her more powerful than she's ever imagined. Desperate to fix her fractured self, Cas dives into the tangled layers of higher mathematics, frantic for numerical power that might not even be possible—and willing to do anything, betray anyone, to get it.

Cas Russell, antisocial mercenary, has decided to Fight Crime. With capital letters, like in one of her friend’s comic books. After all, she has a real-life superpower: with her instantaneous mathematical ability, she can neuter bombs or out-shoot an army. And it’s Cas’s own fault violence has been spiking in the world’s cities lately—she’s the one who crushed the organization of telepaths that had been keeping the world’s worst offenders under control. Now every drive-by or gang shooting reminds Cas how she’s failed, and taking out these scumbags one at a time is never going to be enough. She needs to find a way to stop all the violence. At once. But Cas’s own power has a history, one she can’t remember—or control. A history that’s creeping into the cracks in her mind and fracturing her sanity . . . just when she’s gotten herself on the hit list of every crime lord on the West Coast. Cas isn’t going to be able to save the world. She might not even be able to save herself.