Set about Pole tucking into rotten trout (4,2)
I believe the answer is:
turn to
'set about' is the definition.
(thesaurus)
'pole tucking into rotten trout' is the wordplay.
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'tucking into' indicates putting letters inside.
'rotten' is an anagram indicator.
'trout' is an anagram of 'turto'.
'n' going inside 'turto' is 'TURN TO'.
(Other definitions for turn to that I've seen before include "Result in" , "set about a task" , "Get to work, get busy" , "Consult with" , "Address" .)