Written as a belated treat for the Trick or Treat Exchange. Many thanks to Greenlily for beta-reading.
As told in LOTR Appendix A, "The Kings of the Mark": Éomer and Éowyn's father Éomund died in battle in 3002 of the Third Age, due in part to his own rashness; he rode after a band of Orcs "in hot anger, unwarily, and with few men." Their mother Théodwyn (Théoden's youngest sister) died of an illness soon after "to the great grief of the king. Her children he took into his house, calling them son and daughter." Éowyn was seven years old at the time and Éomer was eleven.
A few months after Éowyn and her brother came to Edoras, their uncle the King rode to inspect the mountain refuge at Dunharrow. Éowyn and Éomer were permitted to go with him.
The King had been very kind to them; when they first entered his hall, he took them by the hands and said he would be as a father to them. Éowyn thought she would rather have her own father back, brave and laughing in his mail and tall helmet, and her own mother, to tell her the tales of shieldmaidens each night before she went to sleep, but she did not say so. She did not say much to anyone.
As for her brother, Éomer seemed content enough at Edoras. When he was at liberty, he ran and scuffled with the other boys in the King's household—as if all was well and nothing had changed, Éowyn thought resentfully. Their older cousin Théodred, the King's son, was there too; Éomer had taken to following him about and hanging on his words, and had nothing but praise for cousin Théodred's new horse or new sword.
Théodred was to ride to Dunharrow with the King, and so of course Éomer agreed to the plan with enthusiasm. Éowyn wasn't sure she wanted to go, but neither did she want to stay in Edoras without her brother—and though she told herself it was foolish, she could not completely silence the quiet voice that whispered, if she let Éomer go without her he might be taken away from her too.
The ride to Dunharrow cheered her, despite herself—there was a wonderful sense of freedom in being on horseback, with the sun warm on her back and the wind in her hair. For a moment she let herself imagine that she could break off from the column and ride all the way back to their house in the Eastfold—that her father and mother would be there to greet her, alive and well, not lying under a green mound covered with simbelmynë.
They reached the hold at last; the ancient walls were high and steep, but the mountains towered higher behind them. Horns were sounded from above, and men shouted to hail the King. The captain who had charge of the hold came forth and knelt before Théoden. Théoden greeted him courteously, then walked along the walls, asking questions about the provisions which were stored there and the state of the fortifications. Éowyn trailed behind. She looked eastward, but the rise of the mountains blocked her view of the Eastfold.
One of the Dunharrow garrison was pointing southward as he spoke to some of Théoden's household from Edoras, and Éowyn turned to listen.
"That's the Dwimorberg," he said, "the haunted mountain." The mountain did have an ominous look to it, looming dark and jagged among its fellows.
Bedric, one of the younger Riders from Edoras, asked doubtfully, "Is it truly haunted?"
"Truly," the Dunharrow man said with a grim look. "The Dead keep it, and on moonless nights they ride abroad and fill all the land with fear."
Bedric looked at him suspiciously. "You are jesting with me," he said.
The Dunharrow man shook his head. "The Dead are there," he said. "I have seen them."
Éowyn walked a short distance away, gazing toward the dark bulk of the Dwimorberg. The Dead are there, he had said. Perhaps her mother and father were there too. They had not been dead so long. And if they weren't, perhaps the Dead would tell her where to find them—if she went and asked it of them boldly.
The way to the mountain was clear enough; she would only have to cross the meadow. She glanced at the others. The Riders' attention was on the King, Éomer was with Théodred, and for that moment, no one was watching her. Éowyn walked backwards very quietly until she was around the corner, and then she ran.
There were a few guards stationed in the green meadow nearby to watch the horses. "Éowyn, where are you going so fast?" one of them called to her with laughter in his voice. Éowyn did not answer, but dashed across the grassy field without stopping. He might tell her uncle, but there was no helping it now.
There was no mistaking the path. It wound upward, lined with dark shapeless standing stones, and an indefinable sense of dread wafted down from it like a cold breeze. Éowyn hesitated. Almost she drew back. But she was a daughter of the House of Eorl; she would not make her kindred ashamed of her. She raised her chin and walked through the first set of black stones.
Nothing dreadful happened, and she told herself that the sense of fear was only meant to make her prove herself worthy. Looking up the path, she let her hand rest against one of the great stones, but snatched it back at once; the stone was ice-cold, though the day was warm. Éowyn shivered and went on.
The path soon grew dark, shadowed by the mountains though it was still full daylight. As she climbed higher, tendrils of mist began to swirl around her. Éowyn almost thought she could see figures in it, human shapes. She blinked hard; the shapes blurred and re-formed but did not vanish. Was that her mother's pale face looking back at her, with her white skirts trailing along the ground? Or higher in the air, the horsehair crest of her father's helmet and the gleam of his spear?
The mist began to gather around her more thickly, and now she could hear voices as well. "Come to us, child, come." The voices that spoke to her seemed a man's voice at one moment and then a woman's, or both blended together. "Do you seek the treasure of the mountain? Long years has it waited there in the darkness! Or do you seek the hidden knowledge of the Dark Years? The Dead possess many secrets. Perhaps you are the fated one. Perhaps it is you."
"I don't want your treasure, or your secrets!" Éowyn almost shouted. "I am Éowyn of the Eastfold. I am here to find my father and mother. Éomund, who was Chief Marshal of the Mark, and Théodwyn daughter of Thengel. Do you know them? Are they here?"
"Perhaps," the voices answered. "Perhaps they are here. Come to us and see. Come closer."
Éowyn squared her shoulders and went on through the mist, between the old black stones. The path was dimmer now; it seemed the light was fading around her. She moved steadily onward as in a dream, hearing the voices call to her and urge her forward.
Suddenly, something jarred her out of her trance. Someone had called her name—not a voice from the mist, but the real, true voice of a living man. She blinked, looking around her. She did not recognize her surroundings; she did not remember having walked so far.
The call came again from behind her. "Éowyn!"
It was her uncle Théoden's voice; after a moment he himself came in sight. He ran to her with a look of relief and caught her shoulders. "Éowyn, sister-daughter. I feared I had lost you."
He was reassuringly warm and solid. Éowyn had not noticed being cold, but now she realized she was shivering, and her hair was damp with droplets of mist.
"Why did you come here, Éowyn? Great danger lies along this path."
"I heard them say the Dead were here. I wanted to find my mother and father." It seemed very foolish once she said it, but Théoden did not laugh.
Instead he said quietly, "Éowyn, your mother and father are not here. They lie in peace beneath their grave-mound. The Dead who haunt this mountain are oath-breakers, who shunned battle. They tell the tale in Mundburg, how the folk of the mountains swore an oath to Isildur to fight for him, and then when he called on them they would not come."
"Oh," Éowyn said. "Then my father is not here. He never broke his word or fled from battle."
"Never," Théoden agreed. "Oaths swore Éomund, all fulfilled them. And your mother was a woman of valor."
He unpinned the golden brooch of his cloak and wrapped her in the thick woolen folds. Éowyn was beginning to feel warm again. It reminded her suddenly of when she ran to meet her father as he rode up to the house, how he laughed and lifted her into the saddle, wrapping his cloak around both of them. To her shame, tears slipped from her eyes and she could not hold them back.
Théoden held her while she wept, and she let herself lean against him. Finally her tears were done, and she sniffed and scrubbed at her eyes.
"Let us go back, Éowyn," Théoden said gently. "Are you tired? Shall I carry you?"
Éowyn found she was weary, as if she had walked many miles. But she shook her head and would not be carried. She walked beside him, holding his hand, and kept her head high. "I will tell you," Théoden said as they walked, "of Baldor son of Brego, who swore to enter the Paths of the Dead." And he chanted the song as they went; Éowyn listened to him and felt her weariness eased.
The mead went round with mirth and laughter
where Baldor sat in his bright-roofed hall . . .
The song told of Brego, the second King of the Mark, and the feast he held to celebrate the raising of Meduseld, the golden hall. Brego's elder son Baldor, heated with wine, made a rash vow to tread the Paths of the Dead. His father, his mother, his brother, and the King's thanes tried to dissuade him, but Baldor refused to be held a coward and forsake his vow; he went off alone into the darkness.
At last Théoden came to the end of the tale:
Long they mourned him and mirth was silent,
for Baldor's son Brego came not
ever again to the golden hall
where his father feasted with his faithful thanes;
in night's shadow beneath the mountain,
in Dwimorberg, the Dead keep him,
till time wears away to the world's ending,
while the long years pass and the land darkens.
Théoden fell silent, and the sound of his voice died away.
"The Dead keep him," Éowyn echoed after a moment. "Would the Dead have kept me too?"
"If you had come to the Dark Door and entered it, Éowyn, then I fear so. They do not suffer the living to pass."
Éowyn raised her chin. "Then it is well that I did not," she said. "I wish to be a valiant shieldmaid and do noble deeds."
They had come now to the last of the dark standing-stones; they passed through and stood once again in the green meadow beside the fortress. Éowyn blinked in the sudden brightness.
Théoden's expression grew lighter, and he looked at her with affection. "Surely you will be a valiant shieldmaid when you are of age," he said. "For there are few even of my Riders who would dare approach so close to the Paths of the Dead!"
Mundburg: the Rohirrim's name for Minas Tirith
"Oaths swore Éomund, all fulfilled them": a line from Tolkien's poem "Völsungakviða en nýja" (The New Lay of the Völsungs) with Éomund substituted for Sigurd. It's also very similar to a line in that was later spoken of Théoden: "oaths he had taken, all fulfilled them" (The Return of the King, "The Muster of Rohan"). In the context of the story, I imagine that Théoden was quoting a line from Éomund's funeral song.