After their second summer in Gravity Falls, the twin's parents decided to let them visit for Christmas. The twins were ecstatic, they get to spend the holidays with their Oregon friends. Mabel gets to hang out with Candy, Grenda, and Pacifica. Dipper, since Soos, Melody, and Abuelita are in Mexico for the holidays, gets to stay with his girlfriend, Wendy! Dipper, even more than Mabel, is excited to share Christmas traditions with Wendy, since she gets out of apocalypse training this year.
Early this morning, Mabel and the girls show up at Wendy's to take her Christmas shopping. Mabel wants it to be a "girls day", so she's won't let Dipper go. "Mabel, I don't want to stay here by myself all day! I want to spend time with Wendy!" "You'll get to tomorrow, Bro-bro." "I'll make it up to you, dude!" Wendy promises. "Ok Wendy." Dipper smiles up at her as she hugs him, and kisses his forehead, causing him to blush, and the girls to Awww.
Dipper thinks 'I'll pick up around the house while Wendy's gone, so she doesn't have to do it when she gets home.' He knows how exhausting it is to go shopping, especially for Christmas, with Mabel. He starts with her room, picking up the clothes off the floor, and just happens to smell her green flannel shirt. It's got the piney, woodsy, girl smell, that's uniquely Wendy. Dipper puts it on over his red T-shirt, and immediately feels comforted about not getting to be with Wendy today. He spends the rest of the day watching TV, playing video games, deciding what to fix for supper, and occasionally catching a whiff of Wendy's shirt.
Meanwhile, typical Mabel, has run the girls ragged. They've been in every store in the Gravity Falls Mall at least twice, and she isn't done yet! She's on a sugar-fueled shopping spree, ready to go all night! Wendy, having bought everything she needs, can't take anymore, and taps out, going home earlier than planned. Leaving Candy, Grenda, and Pacifica to try and wrangle Mabel.
Getting home, she gets out of her truck, and hears that Dipper has the stereo cranked up to 11. Walking into the house, Wendy sees Dipper, dancing around in the living room. Wearing her green flannel shirt. And her jeans. And her boots. And her Trapper's hat. "Dude!" she yells, startling her boyfriend, who looks around, with a horrified look on his face! Wendy wasn't supposed to be home for a few hours, yet here she is, seeing him in her clothes! "Why are you wearing my clothes?!" Dipper, face going pink, as he tries to explain, "I-I Wendy, i-it..." Wendy starts laughing, unable to contain herself, "Dude, at least you aren't wearing my panties!" Dipper's face goes beet-red, and he just looks down at his feet. "Aw duuude!"