A little red engine in the first garden (4)
I believe the answer is:
eden
'first garden' is the definition.
(I've seen this in another clue)
'a little red engine in' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EDEN' is hidden in the letters of 'little red engine'.
'the' acts as a link.
(Other definitions for eden that I've seen before include "The - - Project, Cornwall" , "The best of all gardens" , "The first garden" , "happy state" , "Old Testament garden" .)