Ire of heavenly messenger switching sides (5)
I believe the answer is:
anger
'ire' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for anger that I've seen before include "Hot displeasure; enrage" , "Wrath; annoy" , "exasperation" , "Greatly annoy" , "Emotion" .)