Irritable character in Grahame's story (5)
I believe the answer is:
I believe this clue is a double definition.
'irritable' is the first definition.
'character in grahame's story' is the second definition.
(ratty is a character in the wind in the willows)
(Other definitions for ratty that I've seen before include "Irritable, peevish" , "Wretched" , "Waspish" , "Irritable - Mole's friend!" , "infestation of vermin" .)