Marine vet egregiously returns to house to avenge themselves (3,4)
I believe the answer is:
get even
'avenge themselves' is the definition.
'get even' can be an answer for 'avenge' (getting even is a kind of avenging). I'm not sure about the 'themselves' bit.
'marine vet egregiously returns to house' is the wordplay.
'to house' indicates a hidden word (I've seen 'houses' mean this (part of the clue houses the answer)).
'returns' is a reversal indicator.
'neveteg' can be found hidden inside 'marine vet egregiously'.
'neveteg' in reverse letter order is 'GET EVEN'.
'to' is the link.
Can you help me to learn more?
(Other definitions for get even that I've seen before include "Exact revenge" , "Take revenge" , "Be avenged" , "Throw a twenty, say" , "avoid an odd outcome?" .)