Book I, Chapter 8: "Fog on the Barrow-downs"
The Hobbits are riding away from Bombadil's house when Frodo, suddenly remembering that they did not take their leave of Lady Goldberry, wishes to turn back. When he moves to do so, however, he discovers Goldberry close by, gesturing for them to come to her. They do, and she gives them a blessing for their travels. Frodo is speechless in her presence.
Frodo and his companions journey on, initially making good time, but then succumbing to an unexpected sleep. They awake to find themselves surrounded by fog. They press on in attempt to leave the Barrow-downs and the fog behind them, but Frodo soon realizes he is alone. He hears his friends calling for help in the distance, but he does not know how to reach them. A "deep and cold" voice from a large barrow claims to be waiting for Frodo. The Hobbit is attacked by a large, shadowy figure, whose chilling touch renders him unconscious.
Frodo awakens in a barrow, captive of a Barrow-wight. Sam, Pippin, and Merry are Frodo's fellow prisoners. Around them lies much treasure, but across their necks lies a sword. Frodo is tempted to use the Ring to secure his own escape but not that of his companions; he imagines Gandalf would even approve of such a plan. When his resolve returns, however, Frodo grabs a short sword from the hoarded treasure and attacks a mysterious arm that is creeping its way toward his friends. Frodo severs the arm's hand, but at the cost of breaking the sword. In that moment, Frodo calls to Tom Bombadil for help. Soon, Bombadil arrives, and casts out the Barrow-wight with a song. A second song awakens Sam, Pippin, and Merry. Bombadil gives the company new ponies. Bombadil also enchants the Barrow-wights' hoarded wealth, that it will now be "free to all finders." From the treasure, Bombadil chooses blades for the Hobbits, forged long ago by Men who opposed Sauron. "Few now remember them," Bombadil informs them, "yet still some go wandering, sons of forgotten kings walking in loneliness . . ."
Before taking his leave of them, Bombadil advises the Hobbits to go to the village of Bree and to find an inn called The Prancing Pony. Frodo urges his companions to refer to him as "Mr. Underhill," so as to avoid mentioning the name "Baggins."