Old ship in darkness (3)
I believe the answer is:
ark
'old ship' is the definition.
(as in Noah's ark)
'in darkness' is the wordplay.
'in' says the answer is hidden in the clue.
'ARK' is hidden in the letters of 'darkness'.
(Other definitions for ark that I've seen before include "Noah's vessel - in which the Torah scrolls are kept" , "See 18 Down" , "Coffer" , "The earliest vessel?" , "(E.g. poem) that tells a story" .)