Dismay as prisoner at the back put away (11)

'dismay' is the definition.

'prisoner at the back put away' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'at' is a charade indicator (letters next to each other).
'the back' becomes 'stern' (stern is a kind of back**).
'put away' becomes 'ate' (I've seen this in other clues).
'con'+'stern'+'ate'='CONSTERNATE'

'as' is the link.