Hollow heart in darkish sci-fi warrior (5)
I believe the answer is:
dalek
'sci-fi warrior' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'hollow heart in darkish' is the wordplay.
'hollow' becomes 'dale' (I've seen this in another clue).
'heart in' indicates the central letters.
The centre of 'darkish' is 'k'.
'dale'+'k'='DALEK'
Can you help me to learn more?
(Other definitions for dalek that I've seen before include "Foe of Doctor Who" , "trouble for the doctor?" , "SF villain" , "Croaky-voiced exterminator" , "Robot from Doctor Who" .)