Morwenna was a treacherous black squirrel of Greenreach, the handmaiden of the Starwife.
Morwenna had been plotting for many years to bring ruin to Greenreach and eventually all the land. On the night she put her plan into action, she gave the frail Starwife the final dose of the poison she had been administering to her in the guise of medicine for several days.
At this point she revealed her betrayal to the Starwife, and explained that she had been sewing a cloak woven with spells that she would be using to cover the Starglass and thus cast down the walls of magic protecting the borders of Greenreach. This would allow the enemies of the squirrels, the bats, to attack the realm easily.
Morwenna's plot did allow the bats to attack and destroy Greenreach, but she did overlook something. The Starwife still wore her silver acorn pendant around her neck, and the old squirrel gave it to a falcon who carried it off into the night. Enraged at this, Morwenna killed the Starwife.
Desperate to find the silver acorn so she could unite it with the Starglass and become Starwife herself, Morwenna enlisted the aid of the leader of the bat army, Rohgar, as well as her own, more sinister ally; the High Priest of Hobb.
When both failed to retrieve the silver acorn, Morwenna took matters into her own hands when Ysabelle, the squirrel maiden who had found the pendant after it was dropped from the sky, arrived at Greenreach after her long journey. Pretending to be a friend, Morwenna gained Ysabelle's trust and led her down a long passageway, at the end of which, she said, was the Starglass.
They eventually reached a door. Inside, instead of the Starglass, was a large underground cavern with a large pool of murky water in which lived Morwenna's pet toads. It was at this point that Morwenna stole the silver acorn, left Ysabelle in the cavern, and locked the door, believing that the squirrel maid would be eaten by the toads.
Ysabelle escaped however, and confronted Morwenna on a tree branch of the Hallowed Oak. But as she approached her, the amulet around Morwenna's neck became extremely hot, burning her fur. It was then that Ysabelle realised that Hobb had begun to break through the ground. Ysabelle stared in horror while Morwenna was jubilant-- that is, until she saw the claws of the rat god reaching for her. The High Priest had cursed the wearer of the silver acorn, but not Ysabelle in particular. Hobb blew fire onto Morwenna and she was killed.