From anohter Sherlock Holmes story:
"An instant later our door opened, and a tall young man
entered the room. He was well but quietly dressed in
a dark-gray suit, and carried a brown wide-awake in
his hand. I should have put him at about thirty,
though he was really some years older."

Who knows what a "wide-awake" is?

I believe it's a type of hat - but I know no more than that.

It is also a name given to the sooty tern, but I think it unlikely that he was carrying a sooty tern!

unlikely that he was carrying a sooty tern!
the mental picture caught me off guard and made me choke on my morning tea!

took a tern for the worst, eh?

and got tea all over my soot(y)

Leave no stone unturned, no tern unstoned, no mandrill's stern untoned.

Ha!