Servant to rescue novice inside (5)
I believe the answer is:
slave
'servant' is the definition.
(thesaurus)
'rescue novice inside' is the wordplay.
'rescue' becomes 'save' (saving is a kind of rescuing).
'novice' becomes 'L' (as in a learner driver with L-plates on their car).
'inside' means one lot of letters goes inside another.
'save' placed around 'l' is 'SLAVE'.
'to' acts as a link.
(Other definitions for slave that I've seen before include "Person in bondage" , "One in bondage" , "Person who is owned by someone" , "Bondsman, thrall" , "Forced labourer" .)