The eighth book of the bestselling Rivers of London urban fantasy series returns to the adventures of Peter Grant, detective and apprentice wizard, as he solves magical crimes in the city of London.

Peter Grant is facing fatherhood, and an uncertain future, with equal amounts of panic and enthusiasm. Rather than sit around, he takes a job with émigré Silicon Valley tech genius Terrence Skinner's brand new London start up—the Serious Cybernetics Company.

Drawn into the orbit of Old Street's famous 'silicon roundabout', Peter must learn how to blend in with people who are both civilians and geekier than he is. Compared to his last job, Peter thinks it should be a doddle. But magic is not finished with Mama Grant's favourite son.

Because Terrence Skinner has a secret hidden in the bowels of the SCC. A technology that stretches back to Ada Lovelace and Charles Babbage, and forward to the future of artificial intelligence. A secret that is just as magical as it technological—and just as dangerous.