At home next to the tree, saint having fish, say, to start with (2,3,5,5)
I believe the answer is:
in the first place
'with' is the definition.
Both the definition and answer are adverbs. Maybe there's a link between them I don't understand?
'at home next to the tree saint having fish say to start' is the wordplay.
I cannot quite see how this works, but
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is found in the answer.
'home' could be 'place' (synonyms) and 'place' is located in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'tree' could be 'fir' (fir is a kind of tree) and 'fir' is present in the answer.
'saint' could be 'st' (abbreviation) and 'st' is located in the answer.
The remaining letters 'he' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for in the first place that I've seen before include "originally" , "Where the winner would be" , "Initially" , "for a start" , "Where Adam and Eve lived" .)