Tam Lin is a faerie knight from an old Scottish border ballad. You can see full text of several variants collected by Francis James Child here. He was once human, but was captured by the Queen of Faeries. While a faerie, he impregnates his human lover, Janet, and she rescues him from his fey condition. He and Janet make great NPCs, and his story’s a great plot hook.
The song begins with a warning to the audience: young women must never pass through the wood of Carterhaugh, near Selkirk in the Scottish Borders. An elfin knight lurks in those woods, and he preys upon young women. But Janet, the daughter of a local lord, ignores the warnings. She takes this being, Tam Lin, as her lover. And though he has powers far beyond the comprehension of Christians, she treats him as her equal.
But all is not well with Janet. She falls pregnant, and her father’s retinue is uneasy. When her father gently asks who her baby’s father is, she boldly announces that her lover is an unearthly knight who rides on a steed lighter than the wind. Her father’s court is probably (it’s not explicitly stated) outraged. Not only is Janet unmarried, her lover is some dangerous wood spirit in league with the Devil! Janet flees back to Carterhaugh.
In the wood, Janet tries to pluck an herb that will cause her to miscarry, but Tam Lin suddenly appears and stops her. She begs of him to tell her in Jesus’ name whether he was ever a human and a Christian.
Tam Lin responds with an eerie story. Once, he was a human knight. But when hunting, he fell from his horse. The Queen of Faerie caught him, and whisked him away to her pleasant realm under a green hill. Every seven years, the land of Faerie must pay a tithe to Hell. Tonight is Halloween, and the tithe has come due. And Tam Lin is so fair and full of flesh, he fears that he will be offered as the sacrifice.
(Note: The song’s intended audience probably paid a tithe of all their income to the Church, so it would have made sense to them for faeries, who are not children of God, to pay a tithe to Hell)
But Tam Lin promises this story can still have a happy ending. If Janet can steal her lover from the clutches of the Faerie Queen, he will become a human knight once again.
At midnight, Tam Lin will ride with the Faerie Queen’s procession across England and Scotland. Though there will be many faerie knights, Tam Lin will be the only one riding a white steed. Janet must hide by the side of the road until Tam Lin passes, then rush out and drag him from his horse. The faeries will try to get her to let go by turning Tam Lin into a series of terrible things: an adder, a swan, a bear, a lion, a red-hot iron, and finally a burning coal. Despite their dangerous appearance, none of these things (even the burning coal) will be able to harm Janet. If she holds onto her lover until he turns into a coal, then throws him into a well, he’ll turn into a naked knight.
Janet does as she is bid, and rescues Tam Lin from the Queen of Faerie. The queen is furious. “O had I known at the early morn Tam Lin would from me gone, I would have taken out his heart of flesh and put in one of stone.”
And then the song ends. Perhaps Janet and Tam Lin live happily ever after. Perhaps they live miserable, paranoid lives, always fearing the Queen of Faeries is about to take her revenge. Or maybe the queen kills the two of them dead on the road right then.
At your table, Tam Lin and Janet make wonderful NPCs. They’re memorable, strongly-written, and evocative. If you want to have them on the sidelines of your story (perhaps as allies or rivals of the PCs), they can absolutely work in that role. They also present three obvious plot hooks, one at each stage of their story:
– Janet’s father asks the PCs to figure out where his beloved daughter is sneaking off to every night. Without intending to, the PCs have now involved themselves in the internal politics of the faerie court.
– The PCs encounter Janet on the road on the night of Halloween. She begs their help in rescuing her lover from the Queen of Faerie.
– After having been made human again, Tam Lin begs the PCs to help protect him from the Queen of Faerie, who dwells beneath a hill adjacent to his father-in-law’s lands.
Note, too, that there’s no requirement that Tam Lin be a faerie creature. All the Tam Lin story really requires to work is that Tam Lin be an intimidating being separated from humanity, that he develop a relationship with a human, and that his lover help him (re)become human. For example, in a science fiction game, Tam Lin could be a biological experiment. He was once human, but was forced or tricked into undergoing horrific genetic modifications. He gained great physical and mental abilities, but was so feared by his neighbors that he had to flee. But he befriended and fell in love with a woman who was willing to defy societal convention, battle his wealthy creators, and obtain for him a cure.