Thura was a stoat soldier in Ferahgo the Assassin's horde. He and his "mucker" Dingeye deserted from the horde and ended up at Redwall Abbey. There they were treated with kindness by the peaceful creatures.
During the night, however, the two stoats played around with a bow and arrow and accidentally shot Brother Hal in the neck, killing him.
Frightened, they stole the sword of Martin the Warrior and fled into Mossflower Woods. The blame of Hal's killing fell on Samkim, who found the dead brother after he had picked up the bow.
In Mossflower Woods, Thura contracted a disease called Dryditch Fever and died almost instantaneously, leaving Dingeye to be decapitated by Ferahgo's tracker Dethbrush.
The stoats were gluttonous, and attempted to eat the entire food supply for the Redwall feast. They were eventually stopped and taken to the infirmary, and given something for their stomachs, but as soon as they recovered, they were eating again.
It should be noted that although he and Dingeye never do anything truly good, they were much kinder and friendlier than most vermin, and they were never known to kill intentionally. Also, they were only soldiers of Ferahgo because of their desperation.