Hunt down one poorly written mystery novel (9)

I believe the answer is:

whodunnit

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'written mystery novel' is the definition.
'whodunnit' can be an answer for 'novel'. I also know that 'mystery' relates to this answer.

'hunt down one poorly' is the wordplay.
'one' becomes 'i' (Roman numeral).
'poorly' indicates an anagram (a poor spelling).
'hunt'+'down'+'i'='huntdowni'
'huntdowni' with letters rearranged gives 'WHODUNNIT'.

Can you help me to learn more?

(Other definitions for whodunnit that I've seen before include "yarn unravelled finally?" , "Detective story" , "crime novel" , "literary mystery" , "Mystery drama" .)

I've seen this clue in The Irish Times.

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