Zero Sum Game by Author S L Huang

Book 1 of the Russell's Attic series.

Deadly. Mercenary. Superhuman. Not your ordinary math geek.

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. She can take any job for the right price and shoot anyone who gets in her way.

As far as she knows, she’s the only person around with a superpower . . . but then Cas 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.