Several years ago, Frisk grew tired of what life had given her so she climbed Mt. Ebott, a place that people say no one ever returns. When she got to the top, she tried to investigate a large opening in the ground, but ended up tripping into it. The fall didn't kill her and she found herself in another world. The first thing she ran into was a little Flower. A face appeared on the flower and it introduced himself. "Hi, I'm Flowey! Flowey the Flower." Flowey explained how Souls work in the underground then tried to kill Frisk. Toriel saved Frisk and taught her the ways of the underground. Frisk met many monsters on her journey through the Ruins and met a ghost named Napstablook. Toriel provided a room and pie for Frisk, but her thirst for knowing what else there was in the underground made push on. Toriel tried to get Frisk to stay but her determination to know what else there was hard to fight. Toriel let Frisk go and she entered Snowdin.
She met two Skeletons named Sans and Papyrus. Sans was a funny, lazy guy and Papyrus was the opposite. He gave puzzles to Frisk all the way throughout Snowdin while the Royal Guard, who were all dogs, attacked her as well. Frisk made it to Snowdin town and met many more monsters. Papyrus tried to capture her, but ended up knocking her out. Frisk spent the next couple of days with the two skeletons before she continued on her journey.
She met Monster Kid in Waterfall and saw Undyne on a high ledge. She and Papyrus talked about capturing humans before Papyrus disappeared. Undyne walked to the edge and drew a spear. She hesitated and the spear disappeared, then she disappeared. Frisk and Monster Kid headed through Waterfall until they got separated. Undyne started to chase Frisk. Frisk got caught on the end of a bridge then Undyne destroyed it, sending Frisk falling. After a weird dream, Frisk awoke to in some cold water and she made her way through. She fought a possessed dummy then found Napstablook's house. She listened to some of his music then continued her journey. Frisk met up with Monster Kid again and they continued. They separated again after a while then Frisk ran into Undyne once again. They fought and Frisk ran into Hotlands.
Undyne passed out from heat exhaustion so Frisk went over to a nearby water jug and filled a cup with water, then poured it on Undyne. Undyne got up then left. Frisk went into the lab in Hotlands and met Alphys, who rambled on for a bit before Mettaton crashed in and commenced a quiz show. After Mettaton left, Frisk continued her journey. She met a spider name Muffet, who was doing a bake sale, outside of the lab. Frisk didn't buy anything because it was too high-priced. Mettaton kept attacking Frisk in different scenarios as she went through all the puzzles and Monsters in Hotlands. Then Frisk made it to the core, where she had to do a couple more puzzles before fighting Mettaton. The fight lasted a while before Mettaton ran out of batteries. Alphys came in and found Mettaton on the ground. She stood by Mettaton while Frisk continued.
By this point, Frisk had learned that Alphys had lied to her and she was feeling like she would just let the king of monsters kill her. As she made her way through New Home, Monsters she were familiar with told her a story of how they ended up trapped in their prison and how the prince died. She made it to the king's castle and met Asgore. They were about to start fighting when Toriel came in and once again saved Frisk. Everyone was there From the two skeletons, to Undyne, and to Alphys. It seemed everyone was happy despite still being trapped but then Flowey appeared and took every monsters soul as long as the six human souls Asgore collected throughout the years. Flowey became Asriel, who then became The God of Hyperdeath. There was another long battle and Frisk managed to save all of her friends. After his defeat, Asriel destroyed the barrier. Frisk awoke on the ground as if it were just a bad dream and the monsters now had access to the upper world.
Before leaving Frisk went all the way back to the beginning and tried to convince Asriel to come with her, but he declined. He said he didn't want his parents to see him as how he would turn into. Frisk went back to the end with all the monsters and they all walked out of the Underground together.
After a couple of years the monsters had built up their own city, because humans wouldn't allow them to stay in their city. Frisk had continuous nightmares and ended up getting stabbed by one of her bullies. She got stuck at home, unable to move. Sans and Papyrus watched over her until she got well. After a while, some humans came to try and take Frisk away from the monsters because her bullies claimed that she was the one to attack them. Frisk then met a nice human named Lyona who helped clear up the situation. Frisk, Asgore, and Sans went to court to resolve the issue when things got much worse. Frisk was told that she had to stay there for "not answering questions" even though she told the judge she couldn't speak. Frisk was brought to a place she called "the torture house" and later "hell house" due to things that happened to her there. After escaping from the humans grasp, she ran into a forest and climbed a tree to hide. Unfortunately for her, the branch snapped and knocked her out. When she awoke, she was in the hospital. It became so big that it was across the news. Mettaton came in and interviewed Frisk. When Frisk got better, she was taken back home and things died down. Frisk had Sans accompany her on a trip to Mt. Ebott. She went there to persuade Flowey to come with her to the upper world. It took a bit, but with a little help from Sans, Flowey went with Frisk. After several weeks, Alphys found and built a machine that could split Frisk's soul in two, half for her and the other half for Flowey. It was a long, stressful event but Asriel was back. Frisk had to go back to the humans city to finish the decision on whether or not monsters should be allowed to live there. After that, Frisk had to go to more, far away cities to spread where monsters were allowed to travel.
After Years of going to meetings and dealing with problems along the way, Frisk had grown up, as did Asriel and Monster Kid(now Monster Adult). Frisk made it back home from the final final meeting and was happy to finally relax. When she went to sleep, she awoke in a dream. "Where are we tonight?" Frisk asked. "Looks like the underground." Chara said. Despite Frisk growing up, Chara still remained a child and still dealt with nightmares the same as she did years ago. "Should we go to the beginning?" Frisk asked. "May as well. There isn't anything here." Chara responded. Frisk nodded and they began to walk to the start. Once they made it all the way to the very beginning, they froze. "This... seems familiar." Frisk said. "Yeah but... I can't recall what this is about." Chara said. Inside the room was 6 different figures with their own glowing color. The first was blue, the second was purple, the third was light blue, the fourth was green, fifth was yellow, and sixth was orange.