Xenotime was a trusted witch doctor in a Tollund village. She later convinced King Allanite, Princess Ash, and the people of Tollund that Queen Amethyst was a traitor. After the king left his wife and married Xenotime, she began to raise the dead that had been buried in the bog and use them against her husband. With the king powerless, she locked up the former queen, stripped her step-daughter of her royal title, and sentenced Ash to slave labour in the peat tunnels.
In an attempt to expand her power, Xenotime agreed to a peace treaty to end the wars between Tollund and the neighbouring kingdom of Lindow, if Lindow's Prince Zircon agreed to attend a ball and marry a royal bog woman. After Zircon's plan to marry Ash under Xenotime's nose failed, she beat and tied him up in the middle of town and demanded that Amethyst's diamond shoes be brought to her by midnight, otherwise she would kill Zircon.
The Tenth Doctor recognised Xenotime's witchcraft as a trick in which she'd been using the unique properties of the planet to make it appear as though she wielded great powers. Together with the help of Ash, Root, Mossy, and Professor Lanthanum, the Doctor gave both shoes back to Ash, who used them to destroy Xenotime's bog warriors and reveal her as a fraud.
After Ash resumed her rightful place as heir to the throne, she stripped Xenotime of her title as queen and sentenced her to live out the remainder of her life performing hard labour in the peat tunnels. (PROSE: The Bog Warrior)