Murder by the Clock by Rufus King — Read

There are knocks, Lieutenant Valcour believed, and knocks. He ranged them from gentle careless rappings, through sly sinister taps, to imperative demands and, finally, thumps. He classified the ones at the moment being bestowed upon the hall door as official whacks. He was right. He put the scrap of paper and the crayon pencil in his pocket and turned to greet five men from the station house who flooded into the room on the heels of his "Come in."

They were intelligent-looking young men, well built, alert, and their uniforms were immaculate -- five competent blue jays outlined sharply against gray walls. Lieutenant Valcour knew each one of them both by reputation and by name.