Harry Houdini leaving one in extremes of wonderment and mystery (8)
I believe the answer is:
whodunit
'mystery' is the definition.
(I know that whodunit is a type of murder mystery)
'harry houdini leaving one in extremes' is the wordplay.
'harry' indicates an anagram (harry can mean to attack or spoil).
'leaving' suggests deleting specific letters.
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'extremes' becomes 'wt' (I can't justify this - if you can you should give a lot more credence to this answer).
'houdini' with 'i' taken out is 'houdni'.
'houdni' is an anagram of 'hoduni'.
'hoduni' put into 'wt' is 'WHODUNIT'.
'of wonderment and' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for whodunit that I've seen before include "detective novel" , "Crime story (colloq.)" , "Murderer revealed at the end, US style" , "Question commonly posed" , "thriller" .)