Back by midnight and awestruck (4)
I believe the answer is:
agog
'awestruck' is the definition.
(I've seen this in another clue)
'back by midnight' is the wordplay.
'back' becomes 'ago' (synonyms).
'by' says to put letters next to each other.
'midnight' becomes 'g' (the middle letter in 'night').
'ago'+'g'='AGOG'
'and' is the link.
(Other definitions for agog that I've seen before include "Eager or curious" , "Highly excited in anticipation" , "Very curious to hear" , "Looking amazed" , "Full of excitement" .)