It's not the end of the line for Heimdall.
He had been surprised to find himself alone in a library, until she had slipped through the door that appeared suddenly in the wall and seated herself unobtrusively opposite him.
"I had expected Niflheim to be colder."
"This is not the realm of the dead, though it could be arranged."
Her voice is as expressionless as her face, but the glass-green eyes behind thick spectacles are sharp and focused, and for a moment he is reminded of someone else with the same eyes and a very different smile.
The change is not complete, though there is decay beneath the translucent glow of her face when she speaks of Loki, and Heimdall tries not to avert his eyes from the grinning death's-head he sees when she smiles wisfully in his direction, looking at something invisible to him.
There is a lifetime's worth of reading in the dusty tomes neatly stacked in surrounding shelves higher than he can see: he had heard that Hel had been researching a cure for her affliction, but he rarely sees her in the room. He has been looking for a means to transport Loki to this place without too much disruption to the natural order; so far all the measures described in the books have involved killing the trickster, and he is severely disappointed that she has expressly forbidden this.
"How much time do I have to do this? I hope you're not on a tight schedule."
She had gestured to the clock with broken hands in the corner of the room.
"I'm surprised that your powers of observation fail you in that respect, Heimdall.Time does not pass in the same way here."
"Is that why you live in the past?"
She had not come to the library again for some time.
His attention is drawn to the picture of a train in one of the physics books open on the table: it is a problem about vectors and velocities in the material world, and so completely irrelevant to his purpose. He had been on a train once, when Freyr had complained about being his "cooping himself up and moping all day in the dreary house", and dragged him (protesting and threatening to report Freyr to the police for attempted kidnapping) to the nearest station, from which they had taken a trip to the countryside.
He had stood on a grassy hillside, barely aware of Freyr beside him chattering while unpacking their picnic lunch, and watched his hawk soaring into the endless blue sky. She had returned to him later as a dark silhouette against the golden glow of the setting sun, her familiar weight on his gloved arm as comfortable as the feel of the soft warm ground at his back.
It had perhaps been the closest to contentment he had felt in a situation not involving Loki at his mercy.
There are stories of ghost trains running along their former tracks, sounding and looking exactly as they had in life, reliving their agonizing final moments before disappearing at the precise moment of the fatal crash. The most common theory is that the intense emotions of the dying souls create the physical manifestation of a "psychic imprint".
Heimdall thinks of it as an endless loop of suffering, the perfect vehicle to bring Loki to his waiting daughter.