Number taken in by sweet heroine (5)
I believe the answer is:
ether
'number' is the definition.
(I've seen this before)
'taken in by sweet heroine' is the wordplay.
'taken in by' indicates a hidden word.
'ETHER' can be found hidden inside 'sweet heroine'.
(Other definitions for ether that I've seen before include "Light liquid used as anaesthetic" , "number" , "Chemical solvent" , "What's clear" , "Colourless volatile highly inflammable liquid" .)