The Silkworm (Cormoran Strike Series #2) by Robert Galbraith, J. K. Rowling

Private investigator Cormoran Strike must track down a missing writer — and a sinister killer bent on destruction — in this "wonderfully entertaining" mystery (Harlan Coben, New York Times Book Review) that inspired the acclaimed HBO Max series C.B. Strike.
 
When novelist Owen Quine goes missing, his wife calls in private detective Cormoran Strike. At first, Mrs. Quine just thinks her husband has gone off by himself for a few days — as he has done before — and she wants Strike to find him and bring him home.
 
But as Strike investigates, he discovers that Quine's disappearance is no coincidence. The novelist has just completed a manuscript featuring poisonous pen-portraits of almost everyone he knows. If the novel were published, it would ruin lives — meaning that almost everyone in his life would have motives to silence him.
 
When Quine is found brutally murdered under bizarre circumstances, Strike must race against time to understand the motivation of a ruthless killer, a killer unlike any he has encountered before . . .
 
A compulsively readable crime novel with twists at every turn, The Silkworm is the second in J. K. Rowling's highly acclaimed series featuring Cormoran Strike and his determined young assistant, Robin Ellacott.