The most common and most likely answer to this crossword clue is the 8 plus 6 letter word SHERLOCK HOLMES
I've seen this crossword clue in Independent
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More clues leading to the result SHERLOCK HOLMES
- Head of History in Merkel’s school developed an enquiring mind
- I investigate the underworld or Hell – shocks me appallingly
- ,21 This sleuth, he’ll shock Morse electrifyingly
- Female right to secure houses after intrusion by lecturer and detective
- Detective woman with right advice for combating break-ins, we understand?
Buddy explains!
The straight part
We know that "I investigate the underworld" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i investigate the underworld = sherlock holmes.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.