I immediatly had some sherlock homes-like dark and foggy street in mind, when I saw the topic.
This is what came out so far.
Sherlock isn't there (yet), maybe I'll add him later, I also tried several titles, treating the illo as a bookcover.
The illo was made in freehand and Photoshop, I looked at some photos to find out, how to achieve the typical foggy light and colors.
In the end I used a big fuzzy brush in Photoshop for the colors and tried to avoid big contrasts.
I think, some more details on the wall on the left would be nice.

The whole Illo could be used as a background for a detailed object in the foreground: maybe a lost purse, shoe
or to make it a detective story a knife or a shadow of a person.
or maybe somehting harmless like a cat.
What do you think?
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so here is my second version:
it's darker and features a black cat.





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and a third version, I didn't like the dark colors in the second one, so I got back to the original colors.
and this time: Sherlock Holmes, the mysterious detective himself: