Enid Blyton

"So we'll have to solve the Mystery of Rat-a-Tat House by ourselves!" said Snubby cheerfully. "Oh, well, we're jolly good at mysteries, I think. We've had four already - the Rockingdown Mystery, the Rilloby Fair Mystery..."
"The Rubadud Mystery, " said Diana, "and what was the other? Oh, yes, the Ring o'Bells Mystery."
"We'll call this the Rat-a-Tat Mystery then, as Snubby said, put in Barney. "How queer - they all begin with R."