Beelu was a male water rat under the command of the Marlfoxes. He sneaked into Redwall Abbey with Ascrod, Vannan, and fellow water rat Dakkle while the first battle with the Marlfoxes was occurring outside its walls. The four vermin killed Nutwing the owl, who had spotted them, wounded the three young Redwallers left on guard, and stole the tapestry of Martin the Warrior.
Later, when the other Marlfoxes went out to attack the Abbey a second time, their brother Mokkan stayed behind, saying he was injured. Vannan instructed Beelu to report to her if Mokkan made a suspicious move. However, Mokkan convinced Beelu to help him walk along the riverside; once the pair were out of earshot of the other rats, Mokkan throttled Beelu and tossed him into the stream.