Frank or poor Dan locked up by police (6)
I believe the answer is:
candid
'frank' is the definition.
(I know that frank can be written as candid)
'poor dan locked up by police' is the wordplay.
'poor' is an anagram indicator.
'locked up by' is an insertion indicator.
'police' becomes 'CID' (abbreviation for Criminal Investigation Department).
'dan' with letters rearranged gives 'and'.
'and' going into 'cid' is 'CANDID'.
'or' acts as a link.
(Other definitions for candid that I've seen before include "Blunt; frank" , "Forthrightly sincere" , "Impartial" , "Free and frank" , "Frank, honest" .)