Friday, December 18, 2015. 10:10 PM. Downtown San Francisco, California.

Dipper and Mabel are sitting in the backseat of their mother's car, dressed in their most formal clothing, having just had a fun time at their junior year's Winter Formal. Unlike last year, the event was held at a hotel in San Francisco instead of in the school's gym, and as a result felt much more spectacular to many of the attendants. However, like last year's Winter Formal, Dipper and Mabel went together as a couple. And their classmates still believed them to be the most adorable couple.

"Ha, Wendy would be so jealous!" Mabel playfully teased her brother.

"Come on, she knows. And she actually finds it cute," Dipper replied.

"Cuter than your Lamby Lamb Dance?" Mabel giggled. Dipper jokingly punched his sister's arm, and the two laughed.

The car boarded the I-80 ramp bound to cross the San Francisco-Oakland Bay Bridge towards the East Bay. Even though it is late at night, the traffic is still rather busy.

When Mabel looked away out the window, Dipper bent down, opened his bag, and took out something.

"Hey Mabel, I got something for you," Dipper said.

Mabel turned, and saw her brother holding a hand-knit sweater that says "Best Sister" on it.

"It took all month, and I was still unable to get it perfect," Dipper said, slightly embarrassed. "I just never did knitting before."

Mabel took the sweater and put it on.

"It's perfect the way it is, Dipper. Thank you," Mabel said smiling. She leaned onto her brother.

"Merry Christmas, Mabel," Dipper whispered. He lifted Mabel's head and kissed her cheek.

10:50 PM.

In her room, Mabel is sitting on her bed staring at the sweater Dipper personally knitted for her. She feels really touched, and believes that she should return the favor.

"Dipper has done a lot for me for as long as I could remember, and yet I never actually put the heart to reciprocate it," Mabel said to herself, but also partially to her pet pig Waddles, who is squatting on a cushion beside the bed. "He is willing to sacrifice everything he's worked on for his dumb sibling. It's time I should do the same. But what can I do…"

Waddles squealed.

"Of course! How could it have slipped my mind?" Mabel exclaimed. "Christmas is right around the corner. I should get Dipper a Christmas present!"

Waddles snorted, as if saying, "I told you so."

"But our flight to Auckland departs on the evening of December 22. That will only leave me…four days to find a good gift for Dipper before we leave for New Zealand. Should be plenty of time!"

Waddles oinked two times.

"I'm sorry Waddles, I can't bring you to New Zealand," Mabel said sadly. "So I'm going to have to leave you in the care of one of my classmates."

Waddles snorted. "That's fine with me," he seems to be saying.

Saturday, December 19, 2015. 9:05 AM.

Mabel realized that the task on getting Dipper a secret but perfect Christmas present is easier said than done. She has no idea what she should get for her brother. She decided to contact her Great Uncle Ford to see what he thinks.

After breakfast, Mabel went back to her room, took out her laptop, and video called her great uncles. As the signal tried to reach them, the screen said "Stanley and Stanford Pines. Location: Iceland." A photo of the two as kids building the Stan o' War I serve as their profile picture.

"I wonder what they are doing over there in Iceland," Mabel asked herself.

The screen flipped into an image of Ford, in thick winter clothing, sitting by a makeshift camp set on the slope of a mountain. In the background, Stan is busy shoveling away a pile of snow covering some items Mabel could not identify.

"Hey kid!" Ford exclaimed as soon as he saw Mabel. "Merry Christmas, Mabel!"

"Merry Christmas to you too, Grunkle Ford," Mabel replied. "What's going on back there?"

"We had a little avalanche," Ford said casually. "It's nothing serious. Some of our supplies got buried under the snow, and Stan is trying to dig them out. Anyways, what can I do for you?"

"Oh, well…," Mabel tried to say. "What do you think I should get Dipper for Christmas?"

Ford stroked his chin, as if in thought. "Good question. Well…Dipper does like things that are ultimate. He likes adventure, mysteries, friends…Hey, perhaps you could get him a mystery novel? He sure likes reading those."

"Sounds like a good idea, Grunkle Ford," Mabel brightened up. "He is one book worm. And he especially likes stories involving crime and suspense. Good, good."

"So, any particular title you think you could get him?" Ford asked.

"Well, there is one upcoming book by his favorite mystery author. Dipper is really excited for his next page-turner. In fact, I think it comes out sometime next week, before me and my family leave for New Zealand. I'll have to check."

"You're going to New Zealand?" Ford inquired surprised. "Whoa. Stan and I haven't even been to the Southern Hemisphere yet, though we're planning to someday. You sure do travel a lot, Mabel."

Suddenly the snow pile that Stan was shoveling in the background started trembling. Stan dropped his shovel and inched back, knowing it could collapse at any moment. Just as he was about to take off, the ice mound crashed onto him, sweeping him away. Stan yelled the Wilhelm Scream as the mini-avalanche took him down the slope.

"Uh, Grunkle Ford, shouldn't you help out Stan there?" Mabel asked concerned.

"Nah. Happens all the time," Ford replied nonchalantly. "He'll be fine, probably."

"Stanford!" Stan's desperate voice can be heard.

Ford sighed. "Well, I guess you're right. Talk to you later. Merry Christmas." And with that, the call ended.

Mabel closed the messaging program, and went to search up the exact release date of the upcoming book she had been talking about: The Missing Professor, by Alan Hirsch.

Mabel saw that the book will be released on December 22, 2015; the same day when her family leaves for their vacation.

I could perhaps stop by a book store the morning before we depart, Mabel thought to herself. That shouldn't be so difficult. The only thing I need to do is to keep this a secret from Dipper, and surprise him at the right moment.

Mabel knows a book store in the center of Piedmont, not too far away from the high school. Maybe I could go there right now and see if they will have the book when it gets released, Mabel continued to think. She grabbed her coat and headed downstairs, where Dipper is in the living room having a video chat with his girlfriend.

"Is that, Mabel in the background?" the redhead on the screen asked. Dipper turned and saw his sister about to open the front door.

"Hey Mabel, where are you going?" Dipper asked. "Come and say hi to Wendy!"

"Oh, I, uh…," Mabel stammered. "I just…have something important to do. Hi Wendy okay bye Wendy!"

And with lightning speed, Mabel opened the front door and left the house, leaving Dipper and Wendy confused.

"She doesn't seem to be herself today," Wendy commented. "Usually she would stay and take up the whole chat."

After about a ten minute walk, Mabel arrived at the bookstore, only to find the owner with a suitcase pasting a sign onto the entrance. The sign said: "The bookstore will be closed from December 19, 2015 to January 9, 2016. We apologize for the inconvenience. Merry Christmas and Happy New Year!"

"Mr. Rianda, why are you shutting down the bookstore in that time period?" Mabel inquired.

"Ah, everyone needs a break," Mr. Rianda said as he placed the final strip of tape onto the sign. "I haven't been back to Baltimore for several years; thought I could spend some time with my family for the holiday season."

"Uh, but Mr. Rianda, wouldn't there be a new book coming out next Tuesday?" Mabel asked. "Specifically, The Missing Professor by Alan Hirsch? Wouldn't you want your store to be open for his fans to have first dibs on the new one?"

"I requested not to have any new books delivered until after I get back," Mr. Rianda replied as he bent down to pull out his suitcase handle. "I'm sorry, but I just need to get out of town for once. Merry Christmas!"

And with that, Mr. Rianda went to his car, got in, and drove off.

Mabel proceeded to return home, disappointed. However, as she entered her room, she remembered that another bookstore had opened within Piedmont's borders about a month ago. It should be a twenty-minute walk away, twice the length of time it would take for her to go to the original book store.

I most certainly will have to check out that one this afternoon, Mabel thought as she took off her coat. They should have the new book…

"Mabel? Oh good, you're home!" Mrs. Pines poked her head into Mabel's room, much to Mabel's surprise and annoyance.

"Mom, could you please knock the door before entering?" Mabel mumbled.

"I'm sorry, except that I need to tell you that this afternoon we will be driving over to Pleasanton to spend some time with a friend."

"You mean your college roommate Mrs. Jiménez?" Mabel asked. "Do I have to go? I barely know her or her kids."

"That's because you don't communicate with them often," Mrs. Pines argued. "And yes, you will have to go. We'll be out of town on Christmas, so we might as well get together with a friend beforehand."

After lunch, at around 1:30 pm, Mabel, along with Dipper and their mother, boarded their father's car to head to their friend's place in Pleasanton. As the car backed out of the driveway, Dipper turned his attention towards his sister.

"So, where were you off to this morning?" Dipper asked Mabel. "You acted kind of strangely."

"Oh, yeah, about that…," Mabel said. She does not want to reveal any clues that she wants to get her brother a present. But at the same time, she hates lying.

"Well, this morning, I, uh…I…," Mabel stuttered. "That's not important! What matters is that I am here safe and sound, right?"

"I guess so," Dipper simply shrugged his shoulders. "You probably just met up with a friend or whatever."

"Yeah, heh, heh," Mabel laughed uneasily.

The Pines family stayed over at Pleasanton for the remainder of the day, and they didn't arrive back home until nine in the evening. Mabel decided that she would stop by the backup bookstore tomorrow.

The following morning, Mabel managed to find an opportunity to go to the book store twenty minutes away. She didn't even need to enter the store to find out that they will indeed be selling the new book. There is a poster pasted behind a window with all the upcoming titles for the week, with the day each book will be officially released and start being sold clearly mentioned. And The Missing Professor by Alan Hirsch would start sale on December 22, 2015, the same as its release date.

The next day, Mrs. Pines made Mabel stay home to help pack the stuff the family plans to bring with them to New Zealand and continue on her holiday homework. Luckily for the whole day Dipper did not question Mabel where she went yesterday morning.

Tuesday, December 22, 2015. 1:40 PM.

Mabel spent the entire morning doing more of her Winter Break assignments. After lunch, Mabel finally found an opportunity to leave the house for the bookstore.

"Mabel, where are you going?" Mrs. Pines asked her daughter just as she is about to open the front door.

"Just somewhere," Mabel responded. "Is there a problem?"

"Just, be back before three," Mrs. Pines replied, with a bit of tiredness in her voice. "You will have to wash up, and then we would be leaving for the airport."

"Yes okay I will," Mabel blurted. After her mother turned around, Mabel opened the front door and dashed out.

After entering the bookstore, Mabel looked around, and found the mystery and crime section. She saw what look like the manager put down a box beside an empty shelf. When he pulled out a book from it, Mabel knew immediately that it is what she is looking for.

"Hi, good sir!" Mabel ran up to the well-dressed man. "That book…your store is selling that today, yeah?"

"Yep," the manager responded. "Release date is today. We just got the delivery. You're here just in time."

"Mind if I have a copy?" Mabel asked.

"Sure, take one."

Mabel looked into the box, and decided to pick out a hardcover version of the book. On the eerie-looking cover is a dimly-lit whiteboard with a bloody handprint on it, and beside the handprint are the words "The Missing Professor" in black marker. The name "Alan Hirsch" is scribbled on a wrinkled slip of paper on the marker holder.

Mabel turned to the back cover to read the summary. She's impressed; this is definitely one crime and mystery novel Dipper would like. She then headed towards the front counter.

"Excuse me, ma'am, I would like to purchase this book," Mabel said to the clerk.

The clerk looked up from her phone and saw Mabel. Then she looked down at the table where the novel is placed. She sighed and scanned the bar code of the book.

Mabel proceeded to pay all the necessary expenses. She declined to have the book placed in a bag, and left the store.

Mabel feels satisfied with herself. She finally has something she could give to Dipper, to return the favor of him always sacrificing everything he's done for his dumb sibling.

Mabel continued walking through her neighborhood back home in a half-skipping manner. However, as she approached a corner, she is so lost in thought that she failed to see what is coming. Another teenage girl riding a bicycle crashed into Mabel, knocking over both. Mabel dropped the book she was holding.

"Hey! Watch where you're…Mabel!" the toppled girl shouted. She struggled back to her feet.

"Oh, hi Lucia," Mabel said, dusting herself off. "I'm very sorry."

"Yeah, you should be!" Lucia growled.

Mabel got up and ran towards the book she dropped, only to be tripped by Lucia. Lucia bent down and picked up the book.

"Since when can you read?" Lucia asked mockingly.

"That book is for my brother, Lucia," Mabel said, slightly offended.

"The Missing Professor? Yeah, that sounds like Dipper," Lucia said sourly.

"Give that back, Lucia!" Mabel sprang up and tried to grab the book. Lucia held Mabel down and extended the book further away. She pushed Mabel, causing her to fall back onto the sidewalk.

"Why are you so desperate to get your brother a Christmas present?" Lucia asked. "He's most likely on Santa's naughty list, and therefore, deserves nothing."

With that, Lucia dropped the book into a nearby drainage. The narrow but heavy book slid through the bars and into the sewage. Mabel could hear it plop in the water.

"Merry Christmas, unicorn-girl," Lucia said sarcastically as she got onto her bike and rode away. Mabel painfully stood back up. She doesn't have any more money on her to buy another copy, and it is starting to rain. It would be a bad idea to walk fifteen minutes back to the bookstore in a cold winter storm without an umbrella anyways.

Mabel was drenched by the time she got to her house's front porch. Luckily she isn't wearing the sweater Dipper made for her.

Mabel immediately went upstairs to her room to get some new clothes, and then went to the bathroom to take a shower. Twenty minutes later, she slouched downstairs to the living room, where Dipper is sitting on the couch.

"Oh Mabel, you're home. Didn't realize that," Dipper said. "Hey, is everything all right?"

Mabel didn't say anything. She sat down onto the couch beside Dipper.

"Mabel, what's wrong?" Dipper asked.

Mabel started tearing up. She suddenly buried her face into Dipper's chest and started sobbing. Dipper doesn't know what is troubling his sister, but whatever it is, he can't stand it when she's upset.

Dipper put one arm around Mabel, and pulled her towards him. He stroked her hair as she continued crying into his vest.

It had been a long day of finishing up holiday homework for Dipper. He is very sleepy, and the presence of his sister and being on a soft surface is making him even more wanting to sleep. Mabel feels the same; all she wants to do at the moment is to cuddle against her brother.

Within a few minutes, the twins are asleep, with Mabel pressed against Dipper's chest and Dipper's arm wrapped tightly around Mabel. The two continued snoozing, snuggly holding each other, for some time before their mother told them to wake up and get ready to go to the airport.

"Alright, wake up, you cuties" Mrs. Pines said. "Dipper, go take a shower. Mabel, get your stuff and bring them downstairs."

Thirty minutes later, the Pines family boarded a hired driver's car towards San Francisco International Airport. Dipper is tempted to ask Mabel what is wrong, but decided not to, as she probably needs some time alone. She didn't even say anything when the family dropped off Waddles and the family cat at her classmate's house.

After arriving at SFO, the family met with the tour group they would be accompanying. The family checked in their luggage, cleared immigration, and passed the security check. There is still a long time before boarding by the time the Pines arrived at their gate. Outside the terminal building, the Air New Zealand Boeing 777-300ER they would be taking to Auckland is being catered to by ground staff. Being wintertime, the sun had long set, with the sky dark and the tarmac lit up for the night.

Dipper finally decided to ask his sister what had been troubling her after the two settled down at their gate's waiting area.

"Seriously Mabel, what's wrong?" Dipper asked. "I hate seeing you like this. Please tell me."

Mabel sighed, and looked up at her brother.

"Well…the thing is…it's nearly Christmas, and…," Mabel started. She felt like crying again. "You've always done so much for me, and I was thinking I should return the favor. I had bought the new novel you've been waiting for, thinking that would be a good present."

"You mean The Missing Professor? It's already out?"

Mabel nodded. "It was just released today. I managed to buy a hardcover over at that new bookstore. Except I ran into…Lucia on the way home. She was riding her bike, and she crashed into me. Afterwards, she tossed the book into the sewage. All I wanted to do was, was…to get you…something." Mabel could not hold back her feelings any longer and started crying again.

Dipper pulled Mabel towards him. "That was very sweet of you," he whispered. "I'm so sorry."

Mabel continued weeping as she pulled Dipper's vest to her face. The twins' parents noticed what is going on.

"Is everything all right?" Mrs. Pines asked concerned.

"Just…give her some space," Dipper replied to his mother. Mrs. Pines knew her son is good at comforting her daughter, and decided to let them be.

"I'm really sorry. But please, Mabel, it's okay," Dipper said softly, and kissed Mabel's forehead.

The gesture made Mabel stop crying. She straightened herself and looked at Dipper, with a slight smile.

"You didn't have to," Dipper said. "You already gave me a Christmas present."

Mabel wiped the tears off her face. "What do you mean?"

"You actually give me a present every day," Dipper said, holding Mabel's hand. "And that present is you. The only thing I ask for is you, my sister."

Mabel is touched by what Dipper said. She leaned back onto Dipper's shoulder.

"Then why did you spend your time making me a sweater?" Mabel sniffed. "You would always sacrifice everything you've done for your dumb sibling."

"I want you to be happy," Dipper said. "And you're not my dumb sibling. You're my beloved sibling. And I would do anything for you, because I love you."

Mabel smiled further. "You're my present every day too, Dip," she whispered. "You didn't have to go into all that trouble either. Just you being around with me are a good enough gift for me. I'm serious."

Dipper laughed softly. "Well, thank you."

Mabel pressed herself more against her brother. She lifted Dipper's hand and kissed his palm.

Mr. Pines had been a couple seats down watching the whole thing, just to make sure his kids are all right.

"So…everything settled kiddos?" he asked innocently. "Everything good?"

"Better," Mabel replied.

"Glad to hear," Mr. Pines looked down at his watch. "Ugh. Not even five minutes has passed yet."

The amount of time left until boarding didn't bother the twins. They would never experience boredom as long as the other is with them. Mabel continued leaning on Dipper's shoulder with Dipper's arm around her until the call for their flight from SFO to AKL finally came.

Gravity Falls was created by Alex Hirsch and produced by Disney Television Animation. All characters and related media belong to Disney.