Spoil plan agent has to make a comeback (6)
I believe the answer is:
pamper
'spoil plan' is the definition.
'pamper' can be an answer for 'spoil' (synonyms). I'm unsure of the 'plan' bit.
'agent has to make a comeback' is the wordplay.
'agent' becomes 'rep' (short for representative).
'has' means one lot of letters go next to another.
'to make' becomes 'map' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a comeback' says the letters should be written in reverse.
'rep'+'map'='repmap'
'repmap' backwards is 'PAMPER'.
Can you help me to learn more?
(Other definitions for pamper that I've seen before include "Treat luxuriously" , "Spoil, cosset" , "baby" , "'Indulge, spoil (6)'" , "Treat indulgently" .)