Time passed. I searched diligently, but with growing annoyance. Finally, I shut the last book with a bang. There appeared to be no such place as Kilmorden Castle. Here was an unexpected check. There must be such a place. Why should anyone invent a name like that and write it down on a piece of paper? Absurd!

Another idea occurred to me. Possibly it was a castellated abomination in the suburbs with a high-sounding name invented by its owner. But if so, it was going to be extraordinarily hard to find. I sat back gloomily on my heels (I always sit on the floor to do anything really important) and wondered how on earth I was to set about it.

Was there any other line I could follow? I reflected earnestly and then sprang to my feet delightedly. Of course! I must visit the “scene of the crime.” Always done by the best sleuths! And no matter how long afterwards it may be, they always find something that the police have overlooked. My course was clear. I must go to Marlow.