Complicated situation (4)
'complicated situation' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mess that I've seen before include "pap" , "dirty and unpleasant" , "Dirty or untidy state" , "Officers' restaurant - what a dump" , "dish" .)
(Other definitions for quagmire that I've seen before include "Bog or marsh" , "Bog - impasse" , "Here one is bogged down" , "Boggy ground" , "Bog - awkward situation" .)