Murder Must Advertise

 Peter enjoys working at copy writing which gives him a chance to use words, one of his favourite amusements has always been talking wittily.  He has been talking to Pamela Dean, the sister of the man who died, who had in the past year or so been mixing with an upper-class pleasure-loving set.  He and Pamela were not that well off, so he was "sinning above his station in life" and his mistress  - a member of the Bright Young Things set - was Dian De Momerie, who came from an aristocratic family.  
Peter gets taken to some of their parties, where he goes in fancy dress, as a Harlequin, and Dian takes a strange fancy to him.  He realises that the crowd are taking a lot of cocaine, and he wonders if there is a connection between drug trading and Victor's death.  The young man didn't like drug taking, but was mad about Dian and believed that he would marry her. 

Peter manages to stay under cover in the office, though Miss Meteyard, one of the female copy writers (said to be based on Dorothy herself) is suspicious of him.  He finally solves the case, finding that there is someone at the office who is using the advertisments that go in the paper, to send  messages to dealers throughout London, so that they will know what pub to go to, to pick up their dope. He learns that James Talboys, one of the copy writers, had for some time been doing this for the dope dealers, using the office as a signal depot.. and that Victor Dean had found out and was threatening to expose him.  He had killed Dean by firing a pebble at him from a catapult, while Dean was walking down the stairs. 
Peter feels very sorry for Talboys, who is not long married and has gotten into debt and has just had a baby.  He tells Peter he would give himself up but he doesn't want his wife and child to be pointed at...

Peter suggests that he "takes the gentleman's way out" by putting himself in the line of fire of the drug dealers, who will bump him off....

He is depressed by the ending of the case, though Parker has managed to catch a ring of drug dealers, and he has found out who the killer was.....