As Marco gets out of the shower, Star activates her new wand, but it accidentally knocks Marco, her wand, and her book of spells into her closet. Unable to open the door, Star consults with Glossaryck who suggests she dig deep into her soul to find a solution. Meanwhile, as Marco is advised by Glossaryck to sort out the secrets and stuff in Star's closet. When he finds and starts reading Star's diary, Star panics and unleashes her innate magic, which blasts the door open.
After the destruction of his castle, Ludo is thrown into the cosmos by Star and lands in a forested location. He competes with a giant spider as they go ice fishing. When a bag of potato chips is found, he and the giant spider fight until he wins. He also tames a bald eagle. When he spots Star in the woods, he chases her until he realizes he is back on Mewni. He also obtains a wand of his own which holds the other half of Star's wand magic.
Guidance counselor Mr. Candle tells Star that she is fated to be Queen of Mewni. She has to read her mother's book on how to act like a queen but she gets frustrated and decides to dress up in a more rebellious punk style. Meanwhile, Marco, who is displeased of Candle's career suggestion of being the head janitor on Garbage Island, discovers that Mr. Candle is actually in cahoots with Tom, who planned to ensure "Starco" doesn't happen. He confronts Mr. Candle but is captured by Tom, and must duel Tom to get his freedom.
Marco trains for a red belt in karate. However, after visiting his sensei's home, he discovers his sensei lives with his mother and does not even have a red belt. Sensei explains that he never got to watch the instructional video for the red belt as the tape got jammed in his video player. Marco and sensei visit thrift shops and eventually come across a rare video store where they have to defeat the store owner to win the tape. Meanwhile, Star looks all over the house for a hammer in order to put up a new poster that she just obtained.
Marco teaches Star how to ride a bicycle, but Star does not know how to stop. To make things worse, she refuses to listen to Marco's request to pedal backwards since Marco had tricked Star into thinking he would not let go of the bike. Marco gets a car ride with Oskar as they pursue Star to get her the wand. Glossaryck appears and joins in the fun.
Star throws her wand by accident and it ends up in the mouth of a growling dog who refuses to let it go. She has to take care of the dog and find its owner. Meanwhile, Marco struggles to get a straw into his juice box and has to take care of the laser puppies. She eventually discovers the dog named Willoughby is actually a extra-dimensional being who didn't like life on her planet, so Star has her adopted by a strange lady named Lydia.
After getting a sugar high from seasoning her burrito, Star sets off some magic that accidentally causes a sign to fall and crush a police cruiser. While trying to evade the police, Star encounters a woman by the river bank named Brigid who likes making things out of hair and taking care of injured animals. She later encounters an underwater sea creature who tells her that hiding out is a good thing, but it is revealed the creature is actually her own conscience. Missing her family and friends, she returns to a very worried Marco and turns herself in to the police who have her wash the other squad cars as part of her police-supervised community service.
Star tries to use her wand to clean up the Diaz home before Marco's parents return, but ends up summoning a whimsical cloud that makes an even bigger mess. Meanwhile, Ludo tries to activate his so he can fight off some rats at a tavern. learning that it works when he gets beat up and enraged.
While foraging for donuts that are being tossed at the end of the day, Star encounters Mina Loveberry, a magical girl from Mewni who is Star's idol. Mina has been living as a homeless person on Earth. Star follows Mina and tries to train in her ways, which annoys Marco. At a park, when Mina announces she plans to take over the world, the people decide to hold a vote on whether Mina should rule, and Star is left to break the tie.
Marco wants to show Star the geyser ?Old Youthful? during a Diaz camping trip. King Butterfly joins them on the trip to learn what Earth camping is like. But King Butterfly's antics get him in trouble several times with the park ranger. When Marco reveals he wanted to show Star the geyser, and the ranger says it's likely the last time it will ever erupt, the three try to rush there to see it.
Star and Marco are put in charge of watching Buff Frog's tadpoles. Marco wants to follow the Buff Baby handbook, while Star just wants to cuddle them and poke at them. Things get complicated when the tadpoles sprout their legs and hop around.
While Star and Marco are babysitting his tadpoles, Buff Frog goes on a mission with Boo Fly and other monsters on finding who has been stealing Mewnian corn, but he keeps thinking about his tadpoles during the job, causing him to be a little distracted and klutzy.
Star, Marco, Pony Head, and a bush-themed female named Kelly go to an unidentified dimension to purchase a Goblin Dog (a goblin version of a hot dog). They end up having a hard time when they must deal with the various jobs of the goblin vendor Roy and the many lines that lead to the Goblin Dog truck.
Star has not been following the advices of Glossaryck when it comes to mastering new spells causing the two of them to have a falling out. Marco does various things in order to get Star and Glossaryck to reconcile. Meanwhile, Ludo hears the voices from within the wand that tell him what he needs to master his wand.
Star and Marco compete in the Game of Flags at the Butterfly-Johansen reunion, even though her mother doesn't want her in the game.
When Star gets sent to dentention after a mishap with the school's pet hamster, she meets Janna and other students who got sent to dentention, but one of the students needs help finding the batteries for his TV remote so he can watch a wrestling competition on TV.
Star hosts a sleepover with her girl classmates and Pony Head. They recruit Marco to play a truth or dare game called "Truth or Punishment", where the Truth or Punishment cube administers punishments to everyone when someone lies, and refuses to free everyone until the game is over. The cube's final question is who is their greatest crush. Marco admits he likes Jackie, but the cube gets angrier, insisting someone else is lying. When Star tells the cube that her preferences can change, the cube gets confused and self-destructs. After everyone goes home, the discarded cube springs to life one last time, answering the question about Star's crush.
Star begs Marco to use a Quest Buy gift card before it expires. The Quest Buy sloth tells them that when it expires, they expire.
Marco goes for a visit with Tom in his carriage to go to an 8-hour "Mackie Hands" movie marathon. Soon their friendship changes.
Buff Frog attempts to solve a mystery of a hole in the wall guarding the cornfield when he gets captured by Meat Fork, a humanoid warthog monster with a fork for a left hand. Upon being put to work to grind corn, Buff Frog frees himself to discover who is enslaving the monsters. He encounters the rats as well as Ludo, who offers him Meat Fork's job. Buff Frog refuses and escapes with Meat Fork. Buff Frog decides he will warn Star that Ludo is back.
After Mr. Diaz fails to scare some kids with his haunted house, Star and Janna summon Hungry Larry, reputed to be a very scary spirit, to haunt the house. Janna goes missing and screams attract the kids back to the house. But the kids get scared and go missing; Star and Marco are attacked. Mr. Diaz arrives to find Hungry Larry has eaten everyone, and rescues them.
Spider with a top hat has been entertaining Star's wand monsters at a party. Afterwards, he tries to learn a fighting move where he tries to blast through a wall. Despite getting training from Narwahl and Rock, he is unable to break through the wall. The other monsters are summoned for a fight but they are beaten up. Encouraged by Rock's words, Spider is finally called.to fight a monster.
Star's wand malfunctions, making a mess of her spell casting. Glossaryck tells Star that the way to fix it is to go inside the wand and to fetch the item that does not belong. Star finds that the inside is connected to her memories, but when she gets distracted she loses touch with Glossaryck, and must find the item before her duplicate selves overwrite her past memories. She eventually finds the item in a room highlighting her mother's lineage.
Star, Marco, and Pony Head are about to have a Friendship Thursday by curling up under a blanket on the sofa and watching a television show. Pony Head finds the concept boring and tags along with Marco to pick up a pizza from Emilio's shop. But problems arise when Pony Head gets distracted with buying some skinny jeans, inadvertently confuses a taxi ride with a carjacking, and when Marco makes a casual remark about Emilio's pizza that Emilio takes to heart.
Glossaryck lets Star pick any page in the book to learn some new magic. Star chooses a mysterious chapter, but Glossaryck tells her it is very dark magic and that he will only let her get a short peek at the page. However, Glossaryck is summoned to the Bureau of Magic; he tells Star not to turn to that page, and his consciousness is dragged away into another dimension. While Glossaryck must deal with a not-so-helpful receptionist and has a difficult time getting to the top floor because the magic system is "on the fritz", Star is tempted to turn the page, and enlists Marco to help do it.
Marco shyly tries to ask Jackie Lynn Thomas out on a date, but finds that he is blurting out embarrassing things about himself. He then discovers he has sprouted a small little head out of the side of his neck that is saying all those things. It is a Naysaya, a curse that Tom had placed on Marco so that Marco would not be able to ask out Star. The Naysaya can only go away when it is appeased, so Marco tries giving it what it wants, which is some cereal, but it doesn't go away. Marco meets Jackie again but the Naysaya starts to act up, so Marco decides to spill out all his insecurities in front of Jackie.
Star has second thoughts about attending a dead clown's seance when Jackie asks Marco to go to the school dance with him.
Star tries to find Ludo and retrieve the Book of Spells. She packs a large amount of stuff and goes to Buff Frog, who gives Star and Marco a map of Ludo's hideout. There they find some monsters that have taken over the place but see no sign of Ludo. Star uses the seeing eye spell to find Glossaryck and pleads for him to come back, but he refuses, saying that he has to follow Ludo now.
Star and Marco attend the birthday party for Marco's sensei. Star becomes suspicious of magician-for-hire Preston Change-O, who, after every magic trick he does, seems to be taking something spiritual from the person, and that his hat is becoming longer and longer. She discovers that Preston has the ability to steal joy from people, so she warns him not to do so or else, but Preston does it anyway. When Star tells everyone what is happening, the audience think Star is a spoilsport and ignore her. Sensei talks about his feelings and then informs Star and Marco that he put Preston in the trunk, but when they open it, Preston has disappeared.
Star's parents send a fairy godmother named Baby to evaluate Star, who takes the task seriously, as failing the eval would mean she would have to return to Mewni. At first, Star cleans up her room, shoving stuff in closets or dimensional pockets, but when Baby starts asking Star questions, and things start falling out of the pockets, Star's responses are met with the same neutral phrase "Interesting". followed by jotting down of notes. Meanwhile Marco tries to help Star by bringing Baby food. Baby then asks Star to bring her an apple using magic, but Star fails to do the task despite repeated tries. Baby concludes that Star failed, but Star tries one last time and ends up using the apple seeds to grow an apple tree which drops an apple for Baby. Star's parents learn from Baby that despite not being organized, losing the book of spells, and failing to do simple spells, Star has magic potential way ahead of when her mother was her age, and might even be comparable to Queen Eclipsa.
Marco borrows Star's Dimensional Scissors to find a place to walk the laser puppies, but he soon becomes accustomed to its conveniences, opening a bunch of portals from his bed to access things. Hekapoo, the forger of all of the Dimensional Scissors, pulls Marco into her dimension and confiscates the Scissors as they did not belong to him or Star (Pony Head had stolen them and gave them to Star). Marco must earn the scissors by having to blow out the flame atop Hekapoo's head. Star goes to Hekapoo's dimension to recover Marco, who had chased Hekapoo for 16 years before winning the challenge. When they return, Marco reverts to his teenage body as only a few minutes have passed on Earth time.
Star is called to solve a problem in Miss Skullnick's math class, but she refuses to do it. She tries to cast some magic to get out of it but ends up in a time loop. However with each iteration, the scenario is slightly different. Star goes to Father Time's dimension, but Father Time is too busy to help her, and she gets advice from Omnitraxus Prime, who is in charge of space-time. Star must solve the problem or her world will fall apart.
Pony Head tells Star the bad news that the Bounce Lounge, their favorite partying venue, is closing. Star and Pony Head round up their former Bounce Lounge posse. They start partying and raise enough funds to save the place, however the owner Milly tells them that she is still closing the place because she is tired from having partied over 5,000 years. Afterwards, the Bounce Crew members and Marco take a group picture in a photo booth.
Rhombulus senses an anomaly in the universe's magic, and when he suspects Star is the source he brings them to the Chancellor of the Magical High Commission.
Glossaryck agrees to teach Ludo stuff from the Book of Spells. He first makes Ludo do some physical exercises as Ludo wanted to learn the hard way. Ludo learns and masters a levitation spell and is quite proud of his accomplishment. But when he learns there is a secret chapter that Glossaryck withheld from him but showed Star, he makes Glossaryck unlock them. Ludo reads the forbidden chapter and gains some dark magic, but when he talks with Glossaryck, he now has the voice of Toffee, who has possessed him.
Marco is forced to atone for his behavior toward Miss Heinous when she arrives at his house.
Marco is angry because Jeremy is the person representing the dojo for their karate sensei to become an official karate dojo.
After she destroys the statue of Echo Creek High's mascot, Star must find a way to cheer up the students again.
Star surprises Marco with tickets to a Love Sentence concert, but also invites Jackie. When Star and Jackie start having fun together, Marco starts to feel jealous and wants them to go on without him, but Jackie convinces him otherwise. At the concert Jackie and Marco engage in a kiss, which results in Star running off out of jealousy. As Star leaves the concert, she fires a blast of tainted magic, destroying a billboard.
The songstrell Ruberiot is ordered to write a song about Star for the tradition of Song Day, but Star is reluctant to participate because it portrays princesses as being perfect. Ruberiot ultimately convinces her to let him write a song about the real her, but inadvertently reveals to the people of Mewni that Star lost the book of spells, and that she has a crush on Marco.
At the Echo Creek graduation party, Marco struggles to reconnect with Star after the events of Face the Music. While Queen Moon invades Ludo's new castle with the Magic High Commission, Star is convinced by her friends to ditch the graduation party and instead attend a party with Oskar. Meanwhile, Toffee takes possession of Ludo's body and regrows his severed arm from Ludo's wand, draining the magic of the Magic High Commission and nearly killing Queen Moon. When Star returns, Queen Moon informs her that they will have to leave Earth. Star confesses to Marco about her feelings for him and tearfully leaves him forever.