Upset to find candlestick covered with muck (10)
I believe the answer is:
disconcert
'upset' is the definition.
(disconcerting is a kind of upseting)
'candlestick covered with muck' is the wordplay.
'candlestick' becomes 'sconce' (sconce is a kind of candlestick).
'covered with' means one lot of letters goes inside another.
'muck' becomes 'dirt' (I've seen this before).
'sconce' put within 'dirt' is 'DISCONCERT'.
'to find' acts as a link.
(Other definitions for disconcert that I've seen before include "Disturb, unsettle" , "upset" , "Bother" , "Throw" , "Confuse; worry" .)