Mystery no light has ever been shed on? (4,6)
I believe the answer is:
dark secret
'no light has ever been shed on?' is the definition.
I know nothing about this answer so I can't tell whether this works.
'mystery' is the wordplay.
I cannot quite see how this works, but
'mystery' could be 'secret' (I've seen this before) and 'secret' is found in the answer.
The remaining letters 'dark' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for dark secret that I've seen is " something to hide".)