Beelu was a water rat under the command of the Marlfoxes. He sneaked into the Abbey along with the Marlfoxes Ascrod and Vannan and fellow water rat Dakkle, while the first battle with the Marlfoxes was going on outside the walls. The four killed Nutwing the owl, who had spotted them, wounded the three young Redwallers left on guard, and stole Martin's tapestry.
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 the unfortunate Beelu and tossed him into the stream.