The most common and most likely answer to this crossword clue is the 7 letter word SLEUTHS
I've seen this crossword clue in The Daily Telegraph
S
L
E
U
T
H
S
Buddy explains!

The straight part
We know that "Detectives" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case detectives = sleuths.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 SLEUTHS mean?
SLEUTHS noun- A detective.
- A sleuth-hound; a bloodhound.
- An animal’s trail or track.
- To act as a detective; to try to discover who committed a crime, or, more generally, to solve a mystery.
- Slowness; laziness, sloth.
- A collective term for a group of bears.