Police department holding up lover boy (5)
I believe the answer is:
cupid
'lover boy' is the definition.
'cupid' can be an answer for 'boy' (I have seen 'naked boy' mean 'cupid' so perhaps 'boy' could also mean 'cupid'). I'm unsure of the 'lover' bit.
'police department holding up' is the wordplay.
'police department' becomes 'CID' (abbreviation for Criminal Investigation Department).
'holding' means one lot of letters goes inside another.
'cid' placed around 'up' is 'CUPID'.
Can you help me to learn more?
(Other definitions for cupid that I've seen before include "Boy with wings, bow, arrow" , "a help to Santa" , "Tiny archer as Roman god of love" , "Match-making archer" , "heathen god" .)