He will shortly find underworld (4)
I believe the answer is:
hell
I believe this is a double definition.
'he will shortly' is the first definition.
(common abbreviation)
'underworld' is the second definition.
(synonyms)
'find' acts as a link.
(Other definitions for hell that I've seen before include "Abode of the forces of evil" , "Devil's fiery home" , "One of spelt out words" , "'The road to . . . . is paved with good intentions'" , "Realm of eternal suffering" .)