Following detailed stratagem detective keeps up the average work (5)
I believe the answer is:
plods
'up the average work' is the definition.
I can't judge whether this defines the answer.
'following detailed stratagem detective keeps' is the wordplay.
'following' means one lot of letters go next to another.
'detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'stratagem' becomes 'ploy' (synonyms).
'detective keeps' becomes 'ds' (I can't explain this - if you can you should give a lot more credence to this answer).
'ploy' with its final letter taken off is 'plo'.
'plo' put next to 'ds' is 'PLODS'.
Can you help me to learn more?
(Another definition for plods that I've seen is " Trudges".)