Prisoner on top level said to be hiding away (10)

I believe the answer is:

concealing

I'm a little stuck... Click here to teach me more about this clue!

'hiding away' is the definition.

'prisoner on top level said' is the wordplay.
I cannot really see how this works, but
'prisoner' could be 'con' (abbreviation for 'convict') and 'con' is found in the answer.
'level' could be 'a' (A level is an example) and 'a' is present in the answer.
This explanation may well be incorrect...

'to be' acts as a link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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