Intact, we're told: there's a gap! (4)
I believe the answer is:
hole
'there's a gap' is the definition.
(hole is a kind of gap)
'intact we're told' is the wordplay.
'intact' becomes 'whole' (similar in meaning).
'we're told' indicates a 'sounds like' (homophone) clue.
'whole' sounds like 'HOLE'.
(Other definitions for hole that I've seen before include "Puncture" , "Gap; difficult situation" , "Empty space; aperture" , "Aperture; cavity" , "Aperture; pit" .)