Prisoner, holding a little flower, set to be hung in Tower (8)
I believe the answer is:
carillon
'set to be hung in tower' is the definition.
(a set of bells - they may be hung in a bell tower)
'prisoner holding a little flower' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'holding' means one lot of letters goes inside another.
'little flower' becomes 'rill' (a small stream - something which flows).
'a'+'rill'='arill'
'con' placed around 'arill' is 'CARILLON'.
(Other definitions for carillon that I've seen before include "Chime of bells" , "Set of bells or a tune played on them" , "Set of bells playing melodies" , "Stop" , "sound of bells" .)