The castle was silent. Most of the rooms were empty or abandoned save the royal suite and a single guest room in the east wing where a skeleton lay.
The blankets had been pulled up to his chin. His chest rose and fell peacefully, but his face was set in a pained grimace. His fingers twitched.
His eyes shot open. For a moment the empty sockets glowed with emotion. He sat up and reached for the desk beside him. As his hands closed on the worn leather cover of a book the glow in his eyes faded. He let out a single breath of relief before he pulled the book to him and glanced around the room.
"I shouldn't be here," Sans said. He stood and went to the closet. It was a moment before he remembered he had slept in his clothes from the day before. The only thing left hanging was a black cloak, which he slipped over his head before leaving with the leather book tucked under one arm.
Sans's footsteps echoed up and down the empty corridors as he passed door after door. His bony fingers tapped the book. It almost felt alive.
"Sans?"
He stopped as a young woman stepped in his path. She pulled off her helmet to reveal blue scales and an eye patch. She frowned. "Where are you going?"
"Home."
"Now? In the middle of the night?"
Sans shrugged. "What did you expect, Undyne? I can't get the king or queen to listen to me, and Papyrus shouldn't be left alone for long. But I can trust you to keep an eye on things, can't I?"
Undyne shook her head. "Not now, Sans. If you say something is wrong then I believe you. Tell me what's going on."
Sans hesitated. The leather book felt warm. Undyne wouldn't betray him. Not Undyne, who was alone patrolling the castle even when King Asgore insisted it wasn't necessary.
"Just a feeling," he said. "It's not a grave situation. I still have a bone to pick with the kid, but there's no point to digging for answers."
"Sans . . !"
"But hey, if it makes you feel better you can walk me to the door."
They walked side by side down the dark corridors. They didn't pass anybody else.
"Is Papyrus still-?" Undyne asked, but Sans held up a hand to stop her. They had reached the throne room, but they weren't alone.
lone figure slumped against the Queen's throne, clutching at it with one trembling paw. Dust drifted off of his white fur like starlight. He was wearing his pajamas, eyes closed as his chest fought to rise and fall. Prince Asriel.
Sans ran to the Prince's side. "Asriel," he whispered. He gently took hold of the frail Prince's shoulders. "Asriel, we're here. What happened?"
"Why can't you mind your own business?"
Sans turned at the sneering voice as Undyne gripped her spear. She was standing by the door. Dust trickled from her fingers, but that could have meant anything. It didn't mean she was guilty. He had to know. He had to know now, even if the King and Queen hadn't agreed to a Soul reading.
Her chest glowed. Slowly a deep gray heart stained with rivers of red molten hate emerged to hover between them. Undyne growled. Sans had never seen a human Soul before. They weren't far different from the Souls of monsters. They were even the same color, aside from the red streaks.
"Well?" Undyne asked.
Sans hesitated. As he stared at the Soul he knew how many evil deeds the kid had taken part in. But he also knew how much good she had done. How was it possible? He knew she was involved with the dying Prince; he could sense Prince Asriel all around her. But the reading declared that she was as good and kind as she was bad. The reading couldn't be wrong, could it?
"Sans . . . please . . ."
Sans looked down at the Prince. Tears dripped from his snout. His fingers were starting to dissolve into dust. Sans turned away.
"Sans, is she good or not?" Undyne asked.
"Why even bother asking?" the little girl said. "He's weak. He didn't know what I'm capable of, and now it's too late! Nobody can stop me!"
"I can still stop you," Sans growled.
"No," Undyne said. "Let me handle this, Sans."
Sans's eye began to glow as he grinned. "Kid, I'm the Judge. Stopping you is my job. You, human, will answer for the murder of Prince Asriel."
"Stupid," the human said. "Weak."
She reached into her pocket and drew a knife, but Sans was quicker. He summoned a skull in the air beside him and kept smiling. The skull roared to life and blasted her with a beam of white light. She howled as her Soul was ripped from her body. Sans snatched the Soul from the air, now almost entirely red, and pressed it into the open pages of his book. He slammed it shut. Silence reigned as her body crumpled to the ground.
"Sans," Undyne said softly, "I've never seen . . . Is she in there?"
"Where she belongs," Sans replied. "Where she can't hurt anybody."
Undyne glanced over Sans's shoulder. Her eye widened. "The Prince!"
Sans couldn't reply. Horror seeped into the marrow of his bones. The human was still there, trembling on the ground as she pushed herself to her hands and knees. She shouldn't be alive. She couldn't be. Her Soul . . .
"You can't stop me," she whispered. Her voice was sandpaper, rubbing against his will, scraping away his hope until none was left. "You're a fool, Sans. I . . . can't . . . die. I'll destroy you. I'll destroy you all!"
Her body rippled and vanished, leaving only drifting dust particles and the echoes of her deathly laughter. Sans stood still as the shock of it all sunk it. He had failed. He had taken her Soul, but She was still alive. And She had escaped.
"We're in trouble," Undyne said.