Dark ship in which evil alters (8)
I believe the answer is:
starless
'dark' is the definition.
(I've seen this in another clue)
'ship in which evil alters' is the wordplay.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'in which' indicates putting letters inside.
'evil' is an anagram indicator.
'alters' anagrammed gives 'tarles'.
'ss' placed around 'tarles' is 'STARLESS'.
(Other definitions for starless that I've seen before include "with nobody famous appearing" , "Black" , "Dark" , "Clouded over (of the night sky)" , "like a low-budget movie?" .)