The short begins with the witch inviting an off-screen guest into her cottage. Her crow assumes the guest wants the bear spell, so she tells the story of the man who became the demon bear Mor'du. The man had been the eldest of four sons of a king who lived in an ancient kingdom, all gifted in their own way; the youngest was wise. The third was compassionate. The second was just. And the eldest brother was strong. However, he mistook great strength for character.
One dark autumn, the king grew ill and passed away. Rather than giving the eldest all the inheritance, he divided the rule among all of his sons, believing their gifts combined would make the kingdom even greater. However, the eldest son, feeling disgraced and filled with greed and arrogance, refused to accept this and started a war against his younger brothers after they refused to give total rule of the kingdom to him.
Despite commanding powerful armies, the prince and his brothers were evenly matched. Hoping to turn the tide of the war to his favor, the prince went to the witch for a spell to give him the strength of ten men by offering her his signet ring, and she gave him the spell in a drinking horn, but warns him of making a choice: either he must make amends by reconciling with his brothers or he will suffer a fate trying to fulfill his goal.
When the prince brought his brothers before him by staging up a false truce, to their protests, he drank the spell, which gave him strength tenfold, but to his surprise, in the form of a great black bear. While he would potentially have broken the spell by apologizing to his brothers, the prince instead accepted his new form and slew them in cold-blood.
He then tried to get his army to rule the kingdom, but they saw only the dreaded beast and turned against him. The bear then attacked his former men, slaughtering a great many of them while the rest fled the kingdom in terror. With the armies of the brothers fractured, the kingdom collapsed into darkness and ruin. The bear, now being named as Mor'du for his history, ended up roaming around the area, his once human consciousness now lost forever because of favoring power over the bonds of family.
The witch ends the story here, and offers the spell in the form of a cake to the guest, who turns out to be Wee Dingwall. He panics, says he only stopped by for water, and runs out of the cottage.