The trees at Epsom, of course? (4)
I believe the answer is:
oaks
'the trees' is the definition.
(oak is a kind of tree)
'at epsom of course?' is the wordplay.
'at' is a charade indicator (letters next to each other).
'epsom' becomes 'ak' (I can't justify this - if you can you should believe this answer much more).
'of' becomes 'o''.
'course?' becomes 's'.
'ak' after 'o' is 'oak'.
'oak'+'s'='OAKS'
Can you help me to learn more?
(Other definitions for oaks that I've seen before include "Acorn producers" , "Horse race - trees" , "Hardwood trees" , "Acorn trees" , "material for shipbuilding" .)