Summer vacation in Gravity Falls was over and the twins were back in Piedmont with their lovely parents. They enjoyed being back home and seeing their parents of course, but there were times when they really missed their Grunkle Stan and Ford, who were out adventuring in the ocean and hoped that they would one day get to see them again.

And that wish soon came true.

Dipper had just been playing a new video game he bought, when Mabel entered the room excitedly, holding an envelope in her hands, squealing as if she saw another cute boy or had gotten into Smile Dips again.

"Mabel, what is it?" Dipper asked her, looking very annoyed at being distracted from his game. "I was in the middle of this cool game here!"

"Well that's not better than this!" She exclaimed, holding out an envelope. It had been addressed to the twins and it was in Stan and Ford's writing. "Grunkle Stan and Ford sent us a letter!"

"Whoa!" Dipper gasped. Now that was more interesting. "What's in the envelope?" He began to imagine all the cool things it could possibly be. He smiled just by thinking about it. Maybe they sent a tooth or skin of a creature they captured in the ocean!

"Well, let's find out!" Mabel grinned. She tore open the envelope and found a letter. "Oh my gosh! It's a letter!"

"Well, what are you waiting for?" Dipper asked her, eyeing the envelope in excitement. "Read it! I wanna hear what they say!"

Mabel nodded and looked down at the letter. "Dear Dipper and Mabel..." She skimmed through it and squealed in the end, her eyes widening in happiness. "OH MY GOD!"

"WHAT?! WHAT?! MABEL, WHAT DOES IT SAY?!"

"They're coming, Dipper!" Mabel told him happily. "Stan and Ford said they're doing fine with their travels and they miss us dearly! Their birthday is coming very soon and they want to spend it with us, so they'll come over to Piedmont to see us!"

"Wow!" Dipper gasped when he heard that. "That is exciting, Mabel! It will be really great to see them again! I sure do miss them." Suddenly, his face grew a bit concerned. "Wait... Mabel... did the letter say what time they'll be here? We need some time to prepare for their arrival!"

"Tomorrow at 3 pm!" Mabel smiled.

"WHAT?!" Dipper gasped. He suddenly looked very worried. "Tomorrow! But we won't be ready in time! We need to find a cake, get presents, decorate.."

Mabel placed an arm on her brother and gave him a determined smile. "Hey, don't worry, bro. Together, you and I can accomplish anything! We'll make Stan and Ford's visit and birthday great and get it all set for tomorrow!"

Dipper smiled at his sister and became confident like her. Mabel was right. When working together, they could do anything! And if his sister was confident that they could do it all, then, he was with her.

"You're right, Mabel! Now come on, let's go get ready for Stan and Ford's arrival and give them the best birthday they've ever experienced in their entire lives!" He held out his hand with a grin. "Mystery Twins?"

Mabel returned the gesture. "Mystery Twins!"

The twins excitedly then setted off to get everything ready for their Grunkles' arrival and birthday before they would arrive tomorrow.