Posybud, known as Posy for short, was a pretty young hedgehog; she was kind, and good at healing and cooking, but could not swim.
Posy was captured by Snaggs and his gang, and forced into doing their cooking and other general bidding. When Uggo Wiltud was also captured by Snaggs, he suggested that he and Posy escape. At first, she seemed loath to leave; this was, in fact, due to her knowledge of the vermin's punishment for escapees.
The pair finally escaped together to a makeshift log boat with the help of Jum Gurdy, but he disappeared during a sudden storm. The two hedgehogs nearly drowned, but were found by Razzid Wearat and the crew of the Greenshroud. Posy tried to keep Uggo from revealing too much to the vermin, and it was due to her creativity that they escaped on a raft made of giant crossbow arrows. The Whoomers saved them from the pursuing vermin, and brought them to the hideout of the Fortunate Freepaws, who took them to the Guosim.
The Guosim decided that they should head to Redwall Abbey, to warn the inhabitants of the impending danger. After a bit more adventure, they arrived at their destination and faced the invading Razzid. Posy was inside the Abbey with Uggo when the Wearat started to break into kitchen storeroom. Uggo held the Sword of Martin, but fumbled and lost it after slaying Badtooth. Posy recovered it, and saved Uggo from death by skewering Razzid with the sword.
The Greenshroud was later renamed the Posy Gurdy, in honor of Posy and Jum.