In which Sayers takes yet another turn. Refraining from even trying to marry Lord Peter off -- Harriet Vane is alluded to, once -- she writes a mystery in which Lord Peter himself only slowly comes into view. And provides a gimlet-eyed view of the advertising agency. (The agency where she worked actually put up a plaque commemorating that a fictional employee had been thrown down it.)
It opens with the arrival of a new copy-writer, Death Bredon, at the office of Pym's Publicity, where he is taking the place of an employee who fell down the stairs and, as if evolved, had a half-finished letter to Pym in his desk telling him that someone in his agency was up to something (as if he had put it aside to ponder further). Someone new to the series would still pick up a number of hints that not all that is what is seems, though unlike the first ones it is not chiefly from Lord Peter's point of view (and, not, as in Have His Carcase, because it's in Harriet's, or another point of view that is working with him).
Checking up the dead man's associates also brings him in contact with the high society world of the Bright Young Things, full of drugs, drink, recklessness, and folly, where he adopts the mask of the Harlequin.
It involves a reporter who finds something in his pocket after a stop at a pub, a stone scarab, a game of cricket under an assumed name, the famous Whifflets campaign, customers who are uncommonly picky about the ads (though they like quotations), the etiquette of using other people's ideas, a foolish midnight car race, a jealous young man who's good at writing corset copy, and a woman who has luck at cards after meeting the Harlequin.