A/N: Undertale spoilers through the final ending in this chapter. Be careful, won't you?

"It's almost Halloween," Lupin said, his gentle smile acknowledging the first year Gryffindors, as they sat down in class that Thursday. "And I think as a good a reason as any for a special lesson," He continued. "After all, it's the time of year that people look forward to being scared. What do you think, class?"

There was some nervous tittering and a few wide eyes from some parts of the classroom, but there were also some excited whispers as well. "Ah, I can already hear the word 'Boggart', and that's absolutely right. Mr. Filch has a boggart trapped in a classroom a floor below us. So I think we should go take it on." He adopted a voice that was supposed to be ghostly and spooky, "So bring your bags with you, we may not be coming back."

So saying, he let the class collect their belongings, then led them across the hall and down the stairs, into an unused classroom. Frisk's nose twitched from the musty scent of abandonment. The desks around the room were covered in a thin layer of dust. As Frisk was looking around, the sudden bang of one of the larger drawers at the teacher's desk caused Frisk, and several other students, to jump.

"Remember," Lupin said. "A boggart is a kind of shape shifter that exists to draw out, then feed on, fear that people feel. A boggart can, if it takes the form of a magical creature, 'echo' that creature's magic. But it's drawing on what you think should happen, so the effect was nowhere near as strong as the real thing. For example, a boggart that takes the form of a banshee would not gain a fatal scream." He paused, looking over the class to make sure they understood. "Now, we're all scared of different things," Lupin admonished. "And I know rumors flow like water among you. But please respect your classmates, and nothing you see here goes outside my classroom. Are we in agreement?"

"Yes, professor," the class said in chorus.

"Very good. Now, on three..."

Kevin Duncan stepped up to the line first. Frisk thought she caught a wisp of inky black smoke, but it quickly coalesced into a giant demonic looking black mastiff. When Kevin recited the charm, the dog changed into a poodle, which yapped up at the class.

A roar of laughter went up around the classroom. At Lupin's command, Kevin quickly stepped backward, and the professor called up Wendy Grant. For her, the boggart changed into a pool of red, congealing, expanding, blood on the floor. She took a step backward, and responded with the charm. Instantly, it became a pool of clear reflective water, complete with a tiny sailboat and squeaking rubber ducks.

Adam's boggart was a giant, monstrous looking anthropomorphic blue rabbit that emerged from hiding with a loud roar. With a cool stare and a stable wand, he changed it into a small, blue, plush toy bunny, that looked up at the class with wide eyes.

Caroline faced, of all things, Professor Flitwick. The professor gave her a tutting noise and said that she'd failed to turn in any homework that year, and would be forced to repeat Charms. The charm didn't change Flitwick at all, but the boggart was forced to report that she'd gotten the highest score in the final exam. "Not particularly funny," Lupin commented, "But it's not feeding on any fear from you, and that's certainly good enough."

Frisk was last to face the boggart. She stood, wand in hand, facing the desk. She had racked her for any way to make what she was about to see seem funny, but that had only paralyzed her thoughts more. Every other student had faced some type of creature that had moved to sicken, to attack, to threaten.

The creature that had emerged from the desk did none of those things. He somewhat resembled a human boy. Instead of skin, he had a layer of white fur. His human-like bright green eyes stared directly, desperately, straight at the suddenly paralyzed Frisk. His hands were open, outstretched, and begging. His muzzle was wet with tears.

As the class watched, his head began to shrink, slowly, and large golden petals sprouted around his head. His legs fused together, looking more and more like a plant's stem. And he was shrinking, visibly shrinking.

Frisk was dimly aware that other students were muttering at each other in confusion, and some were giggling. None of them knew what this was, or saw anything remotely scary. They were wondering if someone else been close enough to confuse the boggart. "Help me," the creature called out from behind the desk. "Help me, please!" The voice grew shrill and desperate as the transformation continued. "I... I don't want to go back! Somebody! HELP!"

Frisk's hand went slack and her wand clattered to the floor. She fell to her knees, sobbing uncontrollably, unaware of anything around her. Her heart breaking again, for the one she couldn't save. "I'm sorry," she sobbed. Over and over. "I'm sorry. I'm sorry. I'm sorry."

Because nobody came.

When Frisk finally regained consciousness of her surroundings, she was still slumped on her knees on the classroom floor. The class had left. The only person in the room other than her was Professor Lupin, who was sitting on the floor next to her. The boggart must have still been there too, she could hear the desk rattling.

"Here, you should have some," Lupin said. Frisk wiped her eyes with the sleeve of her robe, and looked up to see him offering her a Cadbury dairy milk chocolate bar. "I've been keeping them on hand with the dementors here. Having chocolate has been useful more than once."

For a second, Frisk thought the sorrow was going to make her lose control again. The last time she'd seen one of these was in Mom's fridge, awaiting another lost soul. She hung onto her composure, barely, emitting something that was an unhappy cross between a laugh and another sob. "Thank you," she whispered. She managed to sit up. She took the candy, unwrapping it hesitantly, and bit off a single square of chocolate.

"Have it all," Lupin said. He watched her eat for a minute or two. "That hit you pretty hard. Would you like to talk about it?"

Frisk stared up at the professor. His face was concerned, and kind, and Frisk badly wanted to talk about it. But she didn't know if she dared. If Mom... or Dad... if they found out she had... she had. She shut her eyes tight, afraid the boggart was going to come at her with a fresh nightmare. "Do you promise," she said finally, "Not to tell anyone?"

"As long as it does not threaten your safety, or the safety of others, I promise not to tell anyone," Lupin said firmly. Was it her imagination, or did she see a sad look in his eyes? "I know what it's like to keep secrets." But she could understand wanting to make sure other people were safe. So she decided to tell him everything. Nearly everything. There was still one part she'd keep to herself.

"Did Ms... Professor McGonagall told you what happened underground?" Frisk asked. Lupin nodded. "She didn't hear the whole story." Frisk took a deep breath, "Have you ever made a mistake so bad, so horrible, that you wanted to go back? To fix it? I have. It was in Waterfall, on a bridge." Frisk could still see it. "The monster child had told me that, 'Undyne told me to stay away from that human. That makes us enemies, or something, right?' I tried to say it didn't... but I don't think he heard me. But he turned, he ran... and he fell, clinging to the bridge. I wanted to go to him, to help him, but Undyne was right there, and I thought she'd attack me when my back was turned. I was so scared."

Lupin's eyes widened slightly, he must have guessed what Frisk was about to say.

"Undyne didn't move either... I think she was thinking the same thing. We both started to move when he cried he was slipping. But we were too late. He fell," Frisk said. "I closed my eyes so tightly. I wanted Undyne to attack me. I thought I deserved it. I wanted so badly to go back in time, to fix my mistake. And I did. When I opened my eyes again, I was in Waterfall town."

"Say that again," Lupin asked.

"I went back in my own history. I went back in time. Everything played out just the same as it did the first time. He told me again, how monsters and humans were supposed to be enemies. He turned and ran, I told him to stop... but he fell again. This time I ran after him. If Undyne struck me, I would have deserved it."

"But she didn't," Frisk said. "and I helped him. I don't know how I got back. And Undyne didn't remember. But Flowey did... he was waiting for me. 'You think you're so clever. But I know what you did. You let him fall. Then you went back, because you regretted it. Heeheehee. You're not the only person who's had that power. To 'Save'. But your desires for this world are stronger than mine. How interesting. I'll be watching.'."

"But that child isn't the one you saw fall, though, was it?" Lupin asked.

Frisk shook her head. She told Lupin what happened the first time she met Asgore. How she had to fight within an inch of her life... and how she almost killed him. How Flowey had finished the job when she refused to kill him. Then how he'd become that nightmarish creature, stealing the other human souls.

"When I defeated him, the souls escaped. He wanted me to kill him. But I couldn't. He looked so miserable. So... lonely. I hid after that. I knew the monsters would blame me for killing Asgore. But Flowey found me again. He told me... he could think of a better ending to my story. I'd have to go back in time. Like I did before. 'Reloading my save', he called it, like it was some sort of computer game. So I shut my eyes, I was determined to find a way to save Asgore... and again, I did... I went back." Frisk scanned Lupins face for signs of disbelief, but she didn't see any.

This time, she didn't just talk about the encounter with Alphys, she told Lupin everything about the True Laboratory. The experiments with determination, the amalgamations, everything. "I'm trying to remember what McGonagall said. The flowers came from the human world, right?"

"They did," Frisk said, "Asriel brought the seeds with him when he passed back through the barrier. They were stuck to him."

"Wait, are you saying..." Lupin said, and his eyes were wide.

Frisk nodded. "Flowey is Asriel Dreemurr. The son of Toriel and Asgore Dreemurr," Frisk said, and the tears had started flowing again. "Flowey is Asriel without a soul." And she finished the story, telling Lupin how Flowey had taken the six human souls, and every single monster soul in the underground, and reconstituted his full body. How they'd fought for control of the timeline... and how Frisk won. Asriel had shattered the barrier, returning the monster souls, freeing the human ones, and confessing he'd turn back into Flowey. "I found him again later," she said, "where I first fell. I think he was waiting to turn back."

"So that's who the boggart was," Lupin said.

"That's not the end," Frisk said. "I wanted to save him so badly. Asriel didn't do anything wrong. He was alive, he was right there. So I went back. I went all the way back. I was going to find something I could change."

"All the way back?" Lupin asked. "Back where?"

"Not where... when. To the time when I first fell," Frisk said, her eyes still leaking. "It's funny, that's what Asriel and I were fighting over, and I gave him his wish anyway. I changed some things, I went back again. I tried more things, I went back again... I think I had everyone convinced I was a time traveler on one cycle or another. The only one who really noticed was Sans, not even Flowey did. I don't know if Sans remembers it all, or he's just a good guesser. But, 'Despite everything, you're still you.' That's what he told me." Frisk's words had gained steam, coming out at a much faster clip.

"On my last try, I thought I had the solution. I even knew it would work. I did everything as close as I could to when I first fell. And when Asriel had returned the souls, I did this." Frisk cupped her hands together, in front of her chest, and focused herself. After a moment, a dark red light shone through her shirt. Her soul, in the form of a bright, vivid, red heart, had emerged. "I'd gotten so used to it being called out in fights with monsters, I could do it myself."

Lupin was staring. Frisk stared too. Whether it was a familiar call, if it was some sort of echo, or just the proximity of Frisk's own soul, Lupin's soul had also come to the surface. His soul was yellow, not the bright yellow of the child's soul that she'd seen in Asgore's bottle, but a paler, more tired looking yellow. And as Frisk watched, it looked like it was being consumed, or attacked, by another more feral brown soul.

"That's your soul?" Lupin asked in amazement. He was apparently unaware his own soul was revealing itself.

Frisk let her focus wane, and both souls disappeared from view. "It is. And I was going to give it up, so Asriel would have a soul. So he could come back. But he didn't take it. He started crying again. 'No, Frisk, you need that soul. I don't want anyone getting hurt for me. I don't like it when people get hurt.' Then he realized how I knew to offer it. 'How many times have you done this?' he asked. I told him that I had lost count, and that horrified him. 'Frisk, you have to live your life!' He grabbed me by my wrists. 'If you really want to be my friend... you won't come back. Promise me! Don't come back!' and I didn't. I... I left him down there. He's still alive. Without a soul. I LEFT HIM! I'm sorry, Asriel, I'm so sorry."

Frisk buried in her head in her hands again as the memory became too much. A moment later, she felt Lupin's hand on her shoulder, patting it to calm her down. Frisk took a deep breath, and looked up at Lupin again.

"Is there anything we can do?" Lupin asked.

"Not unless you know how to give him a soul," Frisk said. When Lupin shook his head, Frisk tried to smile. "I didn't think so."

"Why didn't you bring him – as Flowey – with you? Out from the underground?" Lupin clarified.

"Without a soul, and still having the will to live, he was afraid he'd hurt people. Like he tried to hurt me, like how he had hurt his father." Frisk answered. There was quiet for a moment, as Frisk polished off the chocolate bar. "Watching him turn back into Flowey and not being able to help him..." she started.

"I can understand why being unable to help a friend is terrifying," Lupin said. He held out his hand. Frisk took it, and he squeezed it reassuringly. "And that's why you couldn't tell your parents. How can you tell them that you'd left their biological son behind? You're afraid of what they'd think." Frisk nodded glumly. "I think they'd be proud of you, Frisk. I can't say I've met them, but you did everything you could, right?"

"I guess."

Lupin regarded the young student. "You still think otherwise?"

"Magic itself seems to think otherwise. It keeps reminding me of it, each time I think I've put it behind me. But I can't go back any more. Each time I think about it, I think of all the people with lives that I'm just ripping away. I just can't focus like that anymore, I don't want to."

Lupin opened and closed his mouth, at a loss of words, so after a minute of trying, he gave up. "And maybe you shouldn't. Why don't you go down to dinner, and I'll clean up the boggart?"

"Professor, Lupin, sir," Frisk said. He blinked at her. "When I focused my soul... I could see yours, too. It was under attack, sir. Are you OK?"

Lupin stared at her in amazement, then gave a wan laugh. "I said I knew what it was like to keep secrets, can you keep mine?"

"If it doesn't threaten your safety... or the safety of others," Frisk parroted.

The professor's expression changed, like he wanted to laugh but he couldn't. Then, for a moment, Frisk was convinced Lupin was going to cry. The sorrow was that prevalent in his face. "I guess I have to accept that, don't I? I'm a werewolf. During the three nights of the full moon, I can change into an unthinking, ravenous beast. Professor Snape is giving me a potion to control it, so I don't. Within the wizarding world, it's a horrible stigma. Nobody trusts a werewolf. Almost nobody, that is. Headmaster Dumbledore hired me anyway."

All Frisk knew about werewolves were what she'd read in non-magical stories. That they were one of many horrible beasts that would eat little children if they misbehaved. But Frisk had the chance to meet a lot of monsters in the underground, but they were all nice in their own way.

"And I do too. I think you're a great teacher." Frisk said. She held out her arms again, and Lupin reached out as well, and returned Frisk's embrace.

"Thank you Frisk. How about we go have dinner then?"

They both left to head down to the great hall. The boggart rattled in the desk behind them.

That Saturday, Frisk woke early. She dressed quickly, and headed downstairs for breakfast. She didn't realize it was Halloween until she saw the decorations. As she was eating her eggs and toast, she wondered what costume Toriel would wear, and pictured her in a classic witch's outfit. It actually suited her pretty well. Food finished, she walked quickly to the castle entrance.

The entrance, however, was full of students anxious to get out of the school and start their Hogsmeade weekend. "No first years allowed!" said a familiar blond Slytherin as she tried to make her way into the line. Frisk retreated to the halls edge, remembering McGonagall's warning about keeping a low profile. She waited until the castle's caretaker had let everyone else through.

He looked at her grumpily. "You heard Malfoy. No first years."

Frisk looked back in him in shock. "But... but... my head of house said..."

Behind her, she heard McGonagall's voice. "She's not on your list, Mr. Filch, and that's intended. I'll be seeing her out." The professor gave her a no nonsense look, and waved her toward the door, walking out after her. At least the professor had a brisk walk, as Frisk was having trouble containing her enthusiasm.

She saw Sans first. He was smiling, as always, with his hands in his pockets. He was talking happily with Fred and George Weasley. Papyrus was next, and he gave a modest looking wave. "Hello, friend Frisk!" and then there was...

"MOM!" Frisk exclaimed, racing down the remaining yards, into Toriel's open, waiting, arms.

A/N: Frisk's experiences are predicated on my own Undertale playing, though I only made it three 'Loops' before I realized that you couldn't really change anything after a pacifist true reset and went looking for spoilers on how to save Asriel. You know the outcome of that. So I wondered what would happen if one could change things, how long people would keep looking. I know my answer. If you've enjoyed my writing and are willing to risk my subpar singing, look up my fansong "The One I Couldn't Save" on Youtube (handle: TreguardD) which is based on the same idea. I hope you are enjoying the fiction. -TZ