The most common and most likely answer to this crossword clue is the 13 plus 4 letter word OPEN-AND-SHUT CASE
O
P
E
N
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A
N
D
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S
H
U
T
C
A
S
E
More clues leading to the result OPEN-AND-SHUT CASE
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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.