Tortured saints. Mark may be one of them (6)
I believe the answer is:
'may be one of them' is the definition.
I can't tell whether this definition defines the answer.
'tortured saints' is the wordplay.
'tortured' is an anagram indicator (I've seen this in other clues).
'saints' is an anagram of 'STAINS'.
'mark' acts as a link.
Can you help me to learn more?
(Other definitions for stains that I've seen before include "Discolorations or dirt marks" , "Dirty marks" , "Discolours or dyes wood" , "Discolorations or blemishes" , "Discolourations on satins" .)