The boy returns to eastern valley (4)
I believe the answer is:
dale
'valley' is the definition.
(I know that valley can be written as dale)
'the boy returns to eastern' is the wordplay.
'the boy' becomes 'lad' (informal term for boy).
'returns' is a reversal indicator.
'to eastern' becomes 'e'.
'lad' in reverse letter order is 'dal'.
'dal'+'e'='DALE'
(Other definitions for dale that I've seen before include "Lead into poetic valley" , "Low ground" , "depression" , "Valley, particularly in Northern England" , "An English valley" .)