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 definition 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 am not sure about this - if you are sure you should give a lot more credence to this answer).
'ploy' with its final letter removed 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".)