The end of the summer came more quickly than Dipper had anticipated. It felt like only yesterday they had defeated Bill Cipher once and for all, and now Grunkle Stan was reminding them to pack their bags. Unwilling to hasten their departure, the Pines twins lingered over their suitcases. They spoke very rarely, only to share a sad smile when they found a relic of their adventures- a piece of the McGucket laptop, one of Mermando's bottles. How strange it seemed that they'd spent less than three months in Gravity Falls. They'd already grown accustomed to the musty smell of their attic bedroom.
On the bus ride home, Mabel cried, waving at Wendy and Stan until the Mystery Shack was out of sight. Dipper, on the other hand, stayed in his seat, staring at the floor. He had barely spoken the entire day, and had fallen completely silent once on the bus. Hidden in his vest were xeroxed copies of Journal 3's pages, prepared in secret the night before. He'd left the journal itself at the Shack per his grunkle's request, but the thought of being without its contents was too much to bear. It was the only proof he had of all that had passed.
Mr. and Mrs. Pines greeted their children with hugs, kisses, and a barrage of questions. While there were some things the twins could tell, like how Mabel had won a pig at a fair, they soon realized that much of each story couldn't be shared, how the two of them had stolen a time-travel device from a futuristic stranger the same day. After all, who would believe their tales of magic and horror? No, they could never tell anybody. Mabel and Dipper vowed to keep it a secret, mentioned only when alone together in the dead of night, or when Soos and Wendy texted them. Of course, there was only so much to be said of their time away from home, and when they'd said it all, they stopped bringing it up altogether.
Their first night back, Mabel dragged her sleeping bag into Dipper's room silently. Although neither of them said it aloud, they were both used to sharing a room. For those first couple of weeks, their parents were in awe over how close they'd become over the summer. It was only natural, though. After all, when gnomes pose as humans and child psychics prove to be maniacs, siblings learn to count on one another. But as school started again, the summer bonds that the Mystery Twins had formed wore away. Pretty soon, Dipper slept in an empty room once more.
Mabel adapted to her old life fairly quickly. She'd always been the one to roll with the punches. It was her brother who had trouble readjusting. His mind was still back in Gravity Falls.
Dipper found that he didn't like playing video games as much as he used to. It reminded him of Fight Fighters too much. Instead, he turned to his computer screen more and more, withdrawing from his family as he scoured for even a hint of the supernatural world he'd left behind. Whenever there was a shop proclaiming Psychic Readings! or a museum claiming to show magical knick-knacks, he explored it with Mabel. And often he wondered if his parents ever knew the truth about Grunkle Stan.
Dipper had friends, too. They fawned over the pine tree hat that soon never left his head, and asked him all about Wendy. But they began to notice some changes in him. He was quieter, more serious, and it took more to get him to laugh than it used too. In gym class, everyone discovered that Dipper (and Mabel as well) was much faster and stronger than before, and had much better endurance, thanks to countless times fleeing from monsters. When they pestered him about how that had happened, he'd respond with hesitant tales of Robbie Valentino and chopping firewood. It wasn't the whole truth, the others knew, but they never pressed the issue. No one in school could get Mabel and Dipper to tell all that had happened that one mysterious summer. Whatever it was, everyone agreed that it was something tremendous and horrifying. Both the Pines kids were more cautious, jumped at small noises, and in their eyes was a weary maturity. They'd become guarded.
Still, the summer's events spilled into Mabel's and Dipper's behavior. They both volunteered at the elementary school puppet show, throwing glances at each other the entire time. One night, Dipper convinced his friends to sneak into an abandoned convenience store, and later joined the Boy Scouts. Mabel looked for Lilliputtians at miniature golf courses and tore down her Boyz Crazy posters, claiming that she was too old for them. On her sweaters, strange grotesque creatures appeared.
As the days grew colder, Mabel let that summer become a memory, only thinking of it when she asked her parents if she and her brother could return there when school was over again. But Dipper didn't let go. In fact, the farther away Gravity Falls became, the more he clinged onto the little tidbits he had left of it. By December, he knew the contents of Journal 3 by heart, having read over them when he couldn't sleep at night- which was almost always. He barely hung out with his friends, much to the concern of Mrs. Pines. Dipper was a boy obsessed.
After everything he'd seen, how could he return to such a mundane existence? At least, that's what he reasoned. He'd vanquished demons, fought Gideon in a giant robot, and had come close to death too many times for him to count on his hands. His body has been possessed, and he'd won Globnar! Yet all that meant nothing in the real world. Every great thing Dipper had done could never be told! He was useless without paranatural beings to fight. What good was banishing ghosts if no one believed in them? At Gravity Falls, he'd been a hero, but now? He was nothing.
The change in him didn't go unnoticed by Mabel. At nights, she could see the glow of his bedroom lamp from across the hall, the shaky doodles of gnomes on his school papers. She saw, and she worried.
One night, she caught him trying to summon Bill. Tears slipped down his face as he whispered, "I miss it all so much. How come no one else does?"
Something had to be done. Mabel decided to take action before the problem got worse.
That Christmas, Dipper tore away his sister's haphazardly wrapped gift to find a thick, leather-bound journal, much like the ones at Gravity Falls. She snuck into his room during the night and told him to write down everything he'd seen, make stories out of it. He pretended to be nonchalant, but the next day Mabel saw him slip it into his backpack.
After that, Dipper improved. All of the horror he'd kept to himself spilled out in ink and sweat, disguised as fiction. His teachers fawned over his newfound creativity. One of his tales even made it into the school's literary magazine. He wrote, and he let go.
He made new friends, and reconnected with old ones. Eventually, his laugh came easily again, and the pages of Journal 3 were lost somewhere under his bed. Mabel's heart swelled at his wide, unfettered smile Although Dipper didn't forget his summer in Gravity Falls, it no longer consumed him. He was free.