Cas Russell Books in Order

Zero Sum Game introduces Cas Russell as a Los Angeles mercenary with a very unusual edge. Her brain does impossible calculations on sight, so a hallway, a moving car, or a room full of armed people turns into angles, timing, and survival. She can dodge bullets, land terrifying shots, and think her way through chaos faster than anyone around her.

Math is her superpower.

What makes the series work is that SL Huang does not treat that idea like a gimmick. These books read like near-future thrillers with a noir streak. Cas takes dangerous jobs, trusts almost nobody, and looks at the world with a dry, cutting kind of logic. She is brilliant, violent, and often emotionally off balance, which means the action is sharp but the character work never feels neat or overly heroic.

The deeper Cas gets, the stranger the world becomes. Telepaths, secret organizations, engineered abilities, and missing pieces of her own past all start pushing to the surface. The fallout from the first book keeps echoing through Null Set and Critical Point. Cas wants to solve problems one person at a time, then finds herself pulled into bigger questions about memory, manipulation, free will, and what happens when power is used in the name of doing good.

She is not alone for long. Around Cas, a messy little orbit of allies forms, including the dangerous Rio, the investigator Arthur, the hacker Checker, and later Pilar, who brings a bit of normal life into a world that badly needs it. That slow shift, from loner-for-hire to someone with real connections, is one of the best parts of the series. The friendships matter. So do the arguments, the loyalties, and the ways those people force Cas to see herself more clearly.

Trust is harder for Cas than a gunfight.

If you are starting fresh, the current published order is Zero Sum Game, Null Set, and Critical Point. The series was first self-published under the name Russell's Attic before being revised and re-released in a new order, so that is the path most new readers should follow. Expect fast action, clever premises, and a heroine who is much more interesting than she is easy.