Notes: This is actually based on a Tumblr post! AU. Anna freezes to death and comes back as an undead wight-she can't stop searching for Elsa...

"Do you want to build a snowman?"

At first Elsa thought it was yet another spectre of her imagination, come to plague her. It had been almost a week since Anna was found, frozen nearly solid in the woods outside the castle. No one knew why she was out there. Except Elsa. Her sister had gone out in search of her.

Only she hadn't found Elsa, she'd only found cold and snow and at the very last, the pathetic shelter of a larger-than-usual rock...

Tears brimmed in Elsa's eyes and she dashed them away impatiently.

"Elsa?"

That wasn't her imagination.

She whirled, the hem of her cloak nearly tripping her, and screamed.

Anna stood in the doorway, only it wasn't Anna. Not really. The normally vibrant red hair was an ashy white, and her skin looked blue with cold. There was a greedy light in dull grey eyes.

"Come and play, Elsa," Anna whispered, and smiled at her. Elsa realised with fresh horror that Anna's teeth were stained dull crimson. "It gets so lonely out there..."

"What-what are you doing in here?" Elsa stammered, backing up until her back slammed against the wall, rattling the paintings in their frames. A snowflake pattern of frost spiraled out across the wallpaper, but she didn't notice. "Where's Mum and Dad?"

"They didn't want to play," Anna said, a regretful, creaky sigh escaping her. Blood stained her coat, too, and dripped from the hem of her dress. "But you do, don't you, Elsa? Do you want to build a snowman? None of mine come out right."

"What do you mean?" Elsa asked through stiff, numb lips. Anna turned slightly and something moved in the dim hallway behind her.

"Olaf just doesn't come out right," Anna said. The light in her eyes intensified. "Help me."

"I-I will," Elsa placated, feeling colder than the winter wind still howling outside. "Just...just let me get my coat, Anna, okay?"

"Okay," Anna said agreeably enough, shifting a grey, deadened foot. "You promise?"

"Yes, Anna," Elsa whispered, tears spilling down her face. She barely even realised she'd slipped her gloves off. "I promise."