To show in, I even produced a key (6)
I believe the answer is:
evince
'to show' is the definition.
('evince' can be a synonym of 'show')
'in i even produced a key' is the wordplay.
'in' means one lot of letters goes inside another.
'produced' is an anagram indicator.
'a key' becomes 'c' (I've seen this in other clues**).
'i'+'even'='ieven'
'ieven' is an anagram of 'evine'.
'evine' placed around 'c' is 'EVINCE'.
(Other definitions for evince that I've seen before include "Show, disclose" , "Make evident" , "Venice (anag.)" , "Show or reveal, say interest" , "Indicate, show clearly" .)