Jess Squirrel was the wife of Mr. Squirrel and the mother of Sam Squirrel. She and her family lived in Mossflower when Redwall Abbey came under attack by Cluny the Scourge. Jess and her family came to Redwall after Sam led Matthias there, and they decided to remain there while the battle for Redwall waged.
Jess, with her reputation as a champion climber, volunteered to scale the Abbey to retrieve the Sword of Martin from the weathervane, although she was attacked by sparrows when she reached and forced to climb back down again. She reported that there were old rusty wires where the sword had probably once been, but it was not there. Shortly afterwards, Jess and Basil Stag Hare concocted a plan to retrieve the stolen Tapestry of Martin from Cluny, who was using it as a banner. They traveled to Saint Ninian's, and with distraction, taunts, and a false picture of Martin on a dishcloth they were able to snatch it, passing it to each other like relay runners as they fled. Basil was slightly injured in the escape, so Jess took the false banner and continued to taunt and chase the hordebeasts, taking to the trees.
Cluny himself came to try and wheedle her into giving back the banner; first by offering her a place in his army as his second in command, then with a mixture of threats and false promises about the safety of her family. Jess almost fell to his bait, but decided to play it off as though she believed him and gave him the false banner, then laughed when Cluny saw it was fake. She solemnly reported the loss of the dishcloth to Friar Hugo when she and Basil returned to the Abbey.
During another invasion from Cluny's army, Jess dropped a large barrel filled with angry bees, releasing them upon the rats.
Later, when her son Sam was kidnapped by Slagar the Cruel, she set out with Matthias and Basil Stag Hare to pursue the fox and find her son, and she fought in the battle in the underground city of Malkariss. She was a great help with strategies and climbing trees to help get their bearings.
In the animated series, Jess does not negotiate with Cluny, and she does not throw a barrel full of angry bees at the rats.
Jess Squirrel was a loving wife and a devoted mother, who was willing and able to protect her family from anyone foolish to attack it. She was bold and fierce and quite unafraid of taking on many enemies at once. She delighted in using trickery and cunning to defeat wicked beasts, and was a close comrade of Basil Stag Hare. Jess was also a champion climber of both trees and abbeys. Her battlecry was "Treetops and timber!" She was also good at improvising ways of getting out of tight situations.