Denno was a male mouse who initially resided at Saint Ninian's Church in Mossflower Woods. He later moved to the North Shores with Luke the Warrior's tribe. While he was gathering berries, the rest of the tribe was attacked by Vilu Daskar, and he escaped the massacre. He participated in the attack on the Greenhawk, and later sailed on the Sayna when it left to attack the Goreleech.
Denno was taken prisoner on Volcano Island and rescued by Luke and Vurg. Later, he was one of the four survivors when the Sayna was destroyed. After he was picked up by the Goreleech, he participated in the ruse to fool Daskar into bringing the ship back to the homeland of the mice. He was on the aft of the Goreleech when it sank, and thus survived the sinking of the ship. Later, he traveled to Redwall Abbey and presumably lived out the rest of his life there happily.