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This week’s poser: Dr Watson’s mystifying conundrum

This puzzle has left poor old Watson completely in the dark. Let’s hope you can shed a little light on it for him...

It has long been rumoured that Dr Watson wrote up a good many more of Sherlock Holmes’ cases than the scant number that have appeared in print. I, for one, had always dismissed this as mere wishful thinking on the part of enthusiasts, until that is, I heard about the discovery of a charred piece of manuscript lurking at the bottom of an old trunk by one of the good doctor’s descendants.


The fragment, it appears, came from a draft of one of Holmes and Watson’s less-celebrated adventures, provisionally entitled The Case of the Constipated Clergyman. Why the Strand Magazine deemed it unsuitable for publication, we shall probably never know. All that remains is the following brief but tantalising extract, which sees the two friends returning to London by train from the wilds of North Yorkshire…

‘Confound it!’ I snorted as I threw down the newspaper in disgust.

Holmes, who had been dozing ever since we passed through Doncaster, opened one eye.

‘Problem, Watson?’

‘I just wish that fellow had taken his blasted newspaper with him when he got out at Peterborough!’

‘By “fellow” I take it you mean the recently retired notary with a penchant for cultivating azaleas and more than a passing interest in lepidoptery?’

‘Azaleas? Lepidoptery? The fellow barely uttered a word all the time he was with us! How on earth could you possibly?... By never mind that now! It’s that confounded puzzle in this evening’s Manchester Guardian that’s got my goat!’

Holmes and Watson get down to the nitty-gritty.

Holmes smiled. ‘If you would be good enough to outline the problem Watson, perhaps we shall be able to solve it together.’

I picked up the rather dishevelled newspaper and read out the following:


The Three Electric Light Switches.


‘Electric light switches indeed!’ I scoffed, interrupting myself. ‘Why can’t folks stick with the good old gas mantle like the rest of us?’

Holmes chuckled. ‘One must move with the times my dear fellow. But I suspect the choice of electric lighting is not, of itself, at the root of the matter. Pray continue.’

I read out the rest of the puzzle as requested:


Downstairs in a house are three identical on-off switches. One of them is connected to the light in the attic. The puzzle is to work out which of the three switches controls that light.


The rules are as follows. You are allowed to manipulate the switches as much as you like, and then you are allowed a single trip to the attic. When you are downstairs there is no way to see into the attic, or any of the other rooms the switches might be connected to. Once you have gone up to the attic you are not allowed to go back down to the switches.


How can you tell which switch works the light in the attic?


Whilst I was reading Holmes settled back into his seat and closed his eyes. He remained in that reflective pose for a number of minutes after I had finished, whereupon he opened his eyes again and remarked with a smile:

‘An interesting conundrum, Watson.’

‘But do you have a solution?’

‘Of course- the solution is obvious. So obvious in fact I suspect a good many people would have overlooked it...’


Thus ends the only known fragment of The Case of the Constipated Clergyman. As for the puzzle, have you, like Holmes, managed to find a solution? If not, Alex Bellos of the Guardian explains all here:


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