Entrance prisoner's held at (9)
I believe the answer is:
captivate
'entrance' is the definition.
('captivate' can be a synonym of 'entrance')
'prisoner's held at' is the wordplay.
'prisoner' becomes 'captive' ('captive' can be a synonym of 'prisoner').
'held' indicates putting letters inside.
'captive' going around 'at' is 'CAPTIVATE'.
(Other definitions for captivate that I've seen before include "Fascinate completely" , "Delight" , "Enchant" , "Charm" , "Entrance" .)