Angry, that is about deserter (5)
I believe the answer is:
irate
'angry' is the definition.
(irate can mean angry or annoyed)
'that is about deserter' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'about' indicates putting letters inside.
'deserter' becomes 'rat' (both can mean a traitor).
'ie' going around 'rat' is 'IRATE'.
(Other definitions for irate that I've seen before include "Magical rod" , "become irritated" , "Mad" , "Indignant, angry" , "Wrathful" .)