The Twist Of A Knife by Anthony Horowitz
This is the fourth instalment in the Horowitz/Hawthorne series and in my opinion it is the best one yet.
As a character, Horowitz starts the book breaking off his working relationship with Hawthorne. After the case in book three, Horowitz has had enough and refuses Hawthorne's offer of writing a new book. He decides to focus on his career as a playwright, something he has longed to do for his whole career and he pins all his hopes on the opening night of his West End play. Sadly for Horowitz, things go more than horribly wrong and he is soon on the run from the law, accused of murder. He must go cap in hand to Hawthorne, his only hope of getting out of a mess, but will Hawthorne help now that Horowitz has rejected him?
This is fantastic. It is funny and dark in equal measure. It's full of twists and turns and the characters, as ever are fantastic.