Fail to keep up in time? Wretched! (8)
'wretched' is the definition.
(I've seen this before)
'fail to keep up in time?' is the wordplay.
'fail to keep' becomes 'lose' ('lose' can be a synonym of 'fail to keep').
'up' says the letters should be written backwards (in down clue: letters go upwards).
'in' means one lot of letters goes inside another.
'time?' becomes 'date' (date is a kind of time).
'lose' reversed gives 'esol'.
'esol' put inside 'date' is 'DESOLATE'.
(Other definitions for desolate that I've seen before include "'Bleak, bare (8)'", "Bereft", "Lay waste, despoil", "Crushed by grief", "alone".)