The most common and most likely answer to this crossword clue is the 9 letter word DEMIMONDE
I've seen this crossword clue in The Times
D
E
M
I
M
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D
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More clues leading to the result DEMIMONDE
Buddy explains!

The straight part
We know that "shady group" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shady group = demimonde.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DEMIMONDE mean?
DEMIMONDE noun- A class of women maintained by wealthy protectors; female courtesans or prostitutes as a group.
- (by extension) A group having little respect or reputation.
- (by extension) A member of such a class or group of persons.