The most common and most likely answer to this crossword clue is the 7 letter word MAIGRET
I've seen this crossword clue in The Daily Telegraph
M
A
I
G
R
E
T
More clues leading to the result MAIGRET
- Detective has month in Paris, given welcome after losing heart
- Great, I’m perplexing brilliant solver
- French detective, one appearing in magazine about origin of thefts
- Detective resolves 19 across
- Inspector’s ragtime performance
- In novel form I’m great detective
- I’m great lumbering French detective
- Colleagues upset about independent gross detective
- French solver playing ragtime
- Ragtime-playing detective
Buddy explains!

The straight part
We know that "French solver" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case french solver = maigret.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.