Timmy meets his maternal grandparents, Grandpa Vlad and Grandma Gladys, who host a long and disgusting Yak-filled holiday at his house called "Yaksgiving". After a week of torment, Timmy foolishly wishes they never came to America. He finds himself back in Ustinkistan, his grandparents' native country, with no money or magic to get back home.
It's Yaksgiving and Timmy Turner's grandparents Grandma Gladys and Grandpa Vladislapov are coming over to visit. Timmy remarks that he hasn't seen his grandparents in forever, and doesn't even remember what they look like. Timmy's mother shows him a photo album with a picture of his grandparents, who greatly resemble Timmy and Mrs. Turner albeit much older, and says that they came to America and started up a restaurant that sells yak meat called "Yak in the Box". Timmy exclaims that only a crazy person would eat there. Mr. Crocker is seen there going nuts ordering tons of food and demanding he get a "Yaktion figure" with his order. Back at Timmy's house, the doorbell rings and he rushes to the door to greet his grandparents. He is greeted and then slapped in the face with a seabass, which leaves his face covered in slime. His grandmother exclaims to him "You stink!" and says that it is a customary greeting for Yaksgiving. The gifts they brought for Timmy and his parents (excluding Mr. Turner, who they hate) are turnips, although they gave Mrs. Turner a bigger turnip and Mr. Turner a bag of weasels. Timmy's parents then made him lug his grandparent's heavy luggage up to his room, since they will be sleeping with him since his parents don't want Vlad and Gladys' pet goat eating their stuff. The goat is already chewing on part of the couch.
Grandpa Vlad and Grandma Gladys explain that Yaksgiving is six days long, much to Timmy's chagrin. On the first day of Yaksgiving, they used Timmy's fish bowl to make turnip soup with his fish still inside. On the second day, Timmy walked in on Vlad shaving Gladys' hairy back. On the third and fourth day, Yaks were dropped on Timmy. On the fifth day, a huge stampede of Yaks rushed into the kitchen and crushed Timmy. On the sixth day, Timmy is happy he finally gets to eat after starving for six days, although the food turns out to be extremely gross and in some cases still alive. Timmy is swarmed by bugs from one of the meals and then his grandparent's pet goat grabs him and carries him out of the house while he is chased by Vlad and Gladys' bloodhounds. The goat escapes from the bloodhounds and they turn their attention toward Timmy. Angrily, Timmy wishes that his grandparents had never came to America. Wanda warns him of the danger of this wish, but the dogs are closing in so Timmy demands it be granted. After raising their wands and granting the wish, Timmy ends up in Ustinkistan.
Because Timmy's grandparents never left America, Timmy and his parents end up impoverish and working in the "turnip mines" of Ustinkistan, a bleak and barren country. Even Cosmo, Wanda and Poof are changed, Timmy cannot reverse the wish because Ustinkistan fairies can only grant wishes involving turnips, and when they raise their wands they just shoot turnips at Timmy's face. It starts raining and Timmy says they should go inside, but Wanda tells him in Ustinkistan "inside hasn't been invented yet" and they poof up umbrellas made of turnips. Night time arrives quickly and it stops raining, Cosmo tells Timmy goodnight and they are going asleep for eleven months, because that is how long the nights last in Ustinkistan. Timmy hears wild animals and hides in the leaves of one of the turnips. His fairies tell him that those are the were-wolves that live here, and they "only come out at night". A pair of were-wolves is seen chasing Timmy's parents. Timmy remarks in disbelief that he cannot believe his grandparents love this place, but then he overhears his grandfather crying that he hates Ustinkistan and lives in constant regret of never going to America to start up his Yak in the Box restaurant.
Timmy asks his grandparents why they never left Ustinkistan, they told him they were originally going to board the last ship ever to leave for America called "The Soggy Turnip", a boat made entirely out of turnips. But, "as if by magical spell by selfish buck-toothed boy", they didn't. Grandpa Vlad cries and Timmy's grandparents run off, Cosmo and Wanda appear and tell Timmy they cannot help because they can only grant turnip wishes, so Timmy wishes for a Turnip Time Machine. A giant turnip time machine sprouts from the ground and Timmy uses it to go back in time fifty years. When he first steps out of the time machine, Timmy thinks it didn't work because nothing has changed. Wanda tells him that it worked and not much changes in Ustinkistan. His younger grandparents walk over to him eating yak burgers and talking about their dream, Timmy tells them that they can go to America all they need to do is board The Soggy Turnip. Grandpa Vlad thinks Timmy is an escaped mental patient and is about to hit him with a rock, when Timmy gives Vlad a carving of a Yak in the Box restaurant he made in the future out of a turnip. His grandparents decide to board the ship, and the trio run toward the departing vessel but it leaves just as they reach the dock. His grandparents sadly walk off back to their job at the turnip mines.
Timmy quickly wishes for a Turnip Jetski and his grandparents hop on. Timmy catches up to the boat and jumps the jetski onto a pool on the deck of the ship. With his grandparents safely on their way to America, Timmy is returned to America in his proper time. With Yaksgiving over, Timmy's grandparents come to say goodbye. Vlad and Gladys must return to their normal lives: They rip off their traditional Ustinkistan clothing to reveal white track suits, and pull out expensive electronics to check their stocks, remarking they've just made another million dollars. Timmy realizes that his grandparents are actually very rich, and they tell him that Yak in the Box is a successful restaurant chain. As they leave, Timmy's grandparents whack his parents with seabasses and drive off in a gold SUV. Timmy says that he doesn't believe he is saying it but he will actually miss them. Wanda tells him that he can visit his grandparents at any time. Later on the Turner's go to a Yak in the Box drive-thru where Vlad and Gladys are working. They give Timmy a Yak-tion figure and a special meal to Mr. Turner, a sack of badgers instead of weasels, which he takes as a sign of his in-laws liking him.