The most common and most likely answer to this crossword clue is the 4 letter word NEMO
I've seen this crossword clue in Independent
N
E
M
O
More clues leading to the result NEMO
- Horror film about a submariner
- Previous solution in fiction, one found in movie
- In terms of regular features, he plumbed the depths
- Topless women mounted Verne’s adventurer
- Sign up for a Verne character
- Literary captain raised a warning
- One much sought finding one originally much distraught
- Sub captain’s sign turned around
- In retreat, warning captain of a submarine
- Disney title character writing on the wall from right to left
Buddy explains!
The straight part
We know that "he plumbed the depths" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he plumbed the depths = nemo.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.