"According to Barbarian legend, the world was created when a pine cone fell from the World Tree. All life sprung from its fruit, and still does."
The Immortal Hero Tarnum was woken in the middle of the night by a cry from the Ancestors, telling him to "Save the World Tree". He knew that according to legend, the World Tree was the source of all life in the world, but he didn't know where it was or what it looked like. But he felt compelled to travel northeast, and eventually found the remnants of a barbarian tribe guarding the secret caves in a nearby mountain. Some necromancers had recently fought their way into the caves and never returned, so Tarnum led the tribe after them.
Tarnum sent letters to the five wisest shamans in the area, asking them what the World Tree was and where he could find it. None of them could help him. From a captured necromancer's apprentice, Tarnum learned that the undead had come do destroy the World Tree - the undead despise all living things, so they wanted to strike at the living by destroying that which had given life to the world. Later, Tarnum learned that the necromancers were allied with the barbarian followers of Vorr, one of the Ancestors who had gone insane.
Heading deeper underground, Tarnum eventually came across a strange cavern filled with trees, grass and flowers, even though they were deep underground and there was no sun or rain. Addar, Tarnum's shaman, guessed it was due to the influence of the World Tree. They encountered an elf named Nilidon, who had come to help Tarnum save the World Tree. The elves had known about the World Tree for a long time, and had been its protectors before the job had passed on to the Ancestors. Tarnum asked him where he could find the World Tree, and Nilidon told him he was inside it.
Nilidon explained that Tarnum's confusion came from the inaccurate barbarian translation of the elven name - the elves called the World Tree "the Roots of Life", and the tunnels of the secret caves were like the veins of the World Tree. While Tarnum had been battling the necromancers, they had been spreading a blight on the plants and scorching the rich soil, destroying the World Tree from within. Realizing that the necromancers were closer to their goal than he had believed, he gathered his armies and drove both Vorr and the undead from the World Tree.
"When Tarnum came across a tiny flower growing out of the cracked, scorched earth, he knew the World Tree would recover from the damage done by the Necromancers."