Mickey captivated by this play? (3,9)
I believe the answer is:
the mousetrap
'mickey captivated by this play?' is the definition.
'the mousetrap' can be an answer for 'play?' (I've seen this before). I'm not sure about the remainder of the definition.
'captivated by this play?' is the wordplay.
'captivated by' becomes 'the' (I can't explain this - if you can you should give a lot more credence to this answer).
'this play?' becomes 'mousetrap' (I've seen this before).
'the'+'mousetrap'='THE MOUSETRAP'
(Other definitions for the mousetrap that I've seen before include "Long-running Agatha Christie play" , "Agatha Christie's West End long-runner" , "Murder mystery" .)