Jeff wrote:

Note to tc: FWIW, I've never seen anything either way on this theory, but I
could easily see that portion of _The Valley of Fear_ as an attempt by ACD
to write a detective story that *wasn't* a Holmes. That it got wrapped into
a Holmes story suggests that perhaps his editor/publisher said "Sherlock,
Arthur, the public wants Sherlock"...

I'd have to check my books, but this rings bells as possibly the case.

ISTR ACD wanted to be taken 'seriously' as a 'proper' author and didn't feel Sherlock Holmes was that 'serious' or what he'd be remembered for! Hah! (Or at least, what he wanted to be remembered for.)

So perhaps this was him trying to take a different tack.

Or did I read somewhere that he struggled with novel length fiction - hence the large wodges of back story in at least two if not three of the four novels.

And perhaps further evidenced by all four being a bit 'odd' - eg Hound of the Baskervilles not having Sherlock in it for a great chunk, the flashback you mention above, etc.

I'm about to sleep now, but it's a Bank Holiday here tomorrow so I might get a moment to take a quick look see what I can find.