Null Set: A Cas Russell Novel    by S. L. Huang Order:  USA  Can Tor, 2019 (2019) Hardcover, e-Book     Reviewed by Hilary Williamson Cas Russell is a math genius and a mercenary, on a crime fighting blitz in S. L. Huang's Null Set. In the first entry in this series, Zero Sum Game, she and her associates defeated Pithica, an organization of telepaths intent on making the world a better place - through murder and brainwashing. Now, criminal activities have increased and Cas feels she must do something about it. However, Cas's encounter with Pithica leader Dawna Polk melted her brain, cracking open memories of a past life she knew nothing about. She needs to find out more, in between vigilante crime fighting exploits shared with her tall black partner Arthur Tresting. Their efforts are supported by hacker Checker (who hangs out in the Hole) and by Pilar, who works as receptionist in Arthur's PI office. In an effort to stop the escalation of crime that started after Pithica's defeat, Cas acquires and implements a frequency generation technology developed 'to break up mob violence'. Of course, this has all kinds of unintended consequences that Cas and crew then have to deal with. At the same time, she tries to cope with the effects of recovering memories, and deal with the fact that Rio, whom she could always count on, is now working against her. Cas makes a deal to fix things, but at what cost? This episode ends on a cliffhanger that will leaves fans anxious for more. I enjoyed the action in Null Set but do recommend reading the first book before this one as it's challenging to catch up with the characters and back story if you haven't done so. Note: Opinions expressed in reviews and articles on this site are those of the author(s) and not necessarily those of BookLoons. Find more SF books on our Shelves or in our book Reviews