Phil mocks Keely's new boyfriend Tanner, considering him to be about as deep as a coat of paint. Keely feels he can't handle his best friend having a boyfriend, but Phil grows suspicious of an "8-year-old Bulgarian" girl Tanner is supposedly teaching to read.
Unable to deal with the happy couple of Bradley and Debbie, Pim tells Debbie that Bradley made an advance on her. Things backfire, however, when Debbie implores Pim to help her develop a "bad" attitude to win him back.
Lloyd and Barbara are eager to celebrate Unification Day, to mark the day when the world's countries declared world peace. Phil, however, is torn to choose between the party of the year with his friends and celebrating a holiday with his family.
Pim looks to find a way to cheat her way out of a culinary arts assignment. Deciding the old-fashioned way isn't going to cut it, she chooses to use some future technology to do so. However, she ends up with a bigger problem than she bargained for.
During the night, the Diffys hear a burgular, but see that it is actually a caveman that sneaked onto their time machine, who they name Curtis. Also, Pim is invited to Debbie Berwick's house, for a sleepover, but later tries to get out, literally.
Phil and Lloyd are racing Skyaks, when Lloyd shows him one of the greatest gifts, the afterburner. Phil gets to have the afterburner on one condition; that he babysit Pim while his parents are on the road. While Phil thinks it will be easy, Pim tries to make everything difficult for him. Also, Lloyd and Barbara are not used to the 21st century laws.
During the morning announcements, Tanner can not read Phil's handwriting, and promptly becomes quite embarrassed in front of the school. The head of the news team notices he needs to improve his handwriting, and Phil gets sent back to a second grade class. In the class, he makes a friend, Crash, who turns out to be Tanner's brother. When Tanner finds a video that Crash took of Phil, he decides to put it on air in order to embarrass Phil. Also, Pim uses Debbie to cheat on a anatomy test. Shortly afterward, her conscience starts bothering her.
During detention, Phil starts to talk with a few guys who tell him that he spends too much time with Keely, like they are dating. They also plan to let a bull run during their school dance coming up. After detention, Phil says some mean things to Keely, leaving her hurt. At the dance, Phil and Keely reconcile, and the guys realize tht they got an angry bull, instead of a calm one.
Keely yearns to try out for the upcoming talent competition at her school, but her stage fright stands in the way. Regardless, she tries out and makes it, though only because Phil uses his future technology to help her. Knowing she can't cheat in the finals, she and Phil work together together to overcome her problem.
Meanwhile, Pim and Bradley play parents to a bag of flour for a school assignment.
Pim and Phil are worried that they will become embarrassed when Lloyd is going to play folk music at their school. Also, Barbara takes Curtis to the dentist.
Phil accidentally makes a girl think that he likes her and must find a way to get rid of her. Pim joins the school orchestra to ruin Debbie's solo.
When the time-traveling Diffys realize they are stuck in the 21st century for the time being, they decide to fit in by sending the kids to school. Phil struggles to make new friends with the added difficulty of social status and cliques complicating his new life.
Meanwhile, his sister Pim finds a rival in super-sweet Debbie Berwick, and fights her for the position of chalk monitor.
After Pim uses future gadgets to do chores (and nearly exposing the fact that they are from the future), Lloyd locks up all the future gadgets in the time machine. When Keely is impressed by a gymnast at school, Phil sees a way to get her attention, but will need some future gadgets to help him out.
Pim, bitter that Phil always gets good attention from their parents, sees a golden opportunity to show their parents Phil when he's not at the top of his game.
An upcoming field trip to the tomato farm has Phil worried: at the end of the trip, the students stomp on tomatoes barefoot, and he is worried that if he goes, people will grow suspicious of the fact that he, like every other person from the future, only has four toes.
Pim and Debbie coordinate a fundraiser upon hearing that Mr. Hackett will be undergoing an operation.
Phil and Keely start a doggie daycare to raise money. When they have to babysit an angry dog, they use a futuristic gadget to see what he is saying, and end up becoming good friends with the dog.
Phil, while working on a video productions project with his friends, becomes enraged at them and blows up, causing all of them to leave, which leaves Phil stuck with the task of finishing the project. After having a revelation courtesy of one of his replicates, he seeks to make amends with his friends.
Due to a misunderstanding, Pim is recruited for the H. G. Wells track team.
Debbie creates a goal to create 50,000 cupcakes. Phil finds out that Debbie is a cyborg, but an evil one, and has to try to stop her evil plan.
When Phil and Keely's project, a "plemon" tree, dies, Phil brings out the New-Ager and brings it back to life. Keely is mystified by the New-Ager and takes it and turns herself into a 25-year-old. At school, a depressed Mr. Hackett sees Keely and asks who she is. She tells him that she is a substitue teacher, and she fills in for his class under the alias Ms. Vanderhoosey. After class, Mr. Hackett comes back and asks Ms. Vanderhoosey out, and Phil makes her say yes. He has a plan to interrupt their date, pretending to be her boyfriend, by using the new ager, but his plan goes terribly wrong when he turns himself 75.
At school, Phil sees a girl that he instantly falls for, Alice Da Luca. He finds out that she likes karate, horseback riding, and speaks French, and, on top of that, is also the daughter of the mayor. To impress her, he joins the karate club, and petends to be interested in everything she is. She is so amazed that she invites him to be her date at the Mayor's Ball, where Keely will be working. Meanwhile, at home, Barbara finds out that Pim has anger issues, and signs her up for yoga. Angered, Pim breaks the Wizrd. At the yoga class, she sees that the teacher is none other than the girl who makes her angry, Debbie Berwick. At the ball, Phil starts to act strange, that is because in the wizard, him and Curtis were that last one's whose bodies were switched, and since is was broken, they kept switching back and forth, leaving a mess of the Mayor's Ball.
Everyday, Pim has been making a second lunch, for someone named Jerry. The Diffys think that Pim has a crush. Phil, being curious of who it is, uses the "invisible spray" and sees that it is really a bully. He tells Pim to stand up to her. When Pim does, Jerry goes running to her older brother, Myron, who starts to bully Phil, and orders him to make his lunch. Thinking that Myron is all talk, he does not, and later realizes that he should have made him the sandwhich. Also, Curtis has been stealing the neighbor's lawn ornaments.
Phil and Keely make a pudding dispenser with a milk engine for their science fair project. The only problem is that the milk engine would not invented for a couple more decades. Lloyd becomes afraid that the Diffys will become exposed that they are from the future, and tells Phil he has to move, tonight. Not wanting to move, Phil and Keely sneak into the science fair and try to sabotage their own project.
After failing to make the cheerleading squad, Keely lies to her mother and says that she made it in order to protect her. Instead of telling her the truth, Phil, Keely, and Tia work together to convince Mandy Teslow that Keely is indeed a cheerleader.
Pim, fed up with Debbie's constantly positive attitude, sets out to find just one small thing that Debbie can't stand.
A "friend" from the future, Andy Baxley, shows up in Pickford and offers the Diffys a ride back to 2121. The family is ecstatic, but Phil, knowing Andy's true character, doesn't trust him. Sure enough, Andy's devious side shows through when he blackmails Phil into defacing the statue of the Pickford Friar, the founder of the town. When Phil decides he has had enough, Andy plays a trick on him.
Fed up with their constant bickering, Lloyd imposes on the kids a Versa Day; for the entire day, the kids are forced to swap bodies and walk a mile in each other's shoes to learn a lesson about tolerance. However, the two of them take the spirit of Versa Day in entirely different ways.
Meanwhile, Lloyd helps Curtis to find a job in order to start pulling his weight around the house.
Keely becomes fascinated at the wonders of a futuristic mall after Phil mentions one to her, so he decides to take the two of them on a virtual trip to one. When Keely encounters a charming robot waiter, though, Phil starts to regret the trip.
Pim tries to fit in to various groups after learning the Fashion Zombies didn't invite her to a sleepover, but soon realizes the best course of action is just to be herself.
Mr. Messerschmitt announces a surprise test, which Phil and Keely decide to neglect when the Giggle shows that they both get A's on the test. When the test arrives, they realize that they no nothing on the subject at hand and lose their AV lab privileges as a result of their failure. Keely is worried that due to her cut-off from AV lab privileges, she will not become a successful news reporter in the future, so they check the Giggle, and her hypothesis proves correct. She decides to give up on life, making Phil feel responsible, so he convinces Mr. Hackett to give them a make up test which they must pass to gain their AV lab privileges back.
When Mr. Hackett becomes the Diffy family's new neighbor, Barbara invites him over for dinner to prove they are a typical American family. During the dinner, Lloyd and Barbara get stuck in a time warp, leaving it up to Phil and Keely to save the day. Meanwhile, Pim takes several attempts at selling their house, as she believes they are going to move, since Hackett moved next door.
Phil, looking to get out of more of the girly things Keely has him doing since Via left, introduces Keely to Via, a new student from Britain. However, he starts to question his decision when she starts doing everything with Via and ignoring him.
Barbara, after discovering Pim's room has a startling lack of personality, sets out to redecorate it. Pim however, has her own ideas of how her room should be decorated.
Keely asks Phil to the dance with encouragement from Via, and he accepts. They are both really anxious to go with each other, though Phil soon receives notice that his father has fixed the time machine and they will be returning home. He lets Keely know, who asks Owen out since Phil won’t be able to attend. Lloyd discovers that he has much more work to do on the time machine, and that Phil will be able to go with the dance with Keely, though she becomes upset with him that he could leave at any given time without notice.
Meanwhile, Pim, knowing that she’ll be moving and won’t be able to attend the dance, lies, saying that she’s got a boyfriend from Handsome Town, though he won’t be able to come, as she’s moving. When word gets out that she’s not moving, she much find a date, otherwise she’ll look like a fool in front of the Fashion Zombies.
It's Career Day, and Phil cannot decide on a job during the assembly. After seeing the creator of the WIZRD in his classroom taking the Career Placement Test, he realizes that the test is wrong, as it will not tell you what you are going to do, and therefore decides not to take the test, placing him in detention.
Pim, however, takes an interest in becoming a police officer.
H.G. Wells will be burying a time capsule, and the students have to place one object of their’s into the capsule, which won’t be dug up for years to come. Lloyd notices the things that are going into the time capsule and realizes that on a date with Barbara, he and she found a time capsule, which they dug up and went through. He realizes that if they write a letter and place it in the time capsule telling their future / past selves not to buy a time machine, they will have never left the future, and thus would be home. Everyone is excited, though Phil knows that if he never went to the past, he would have never met Keely, and all of his memories about her would be gone.
Phil and Keely are really anxious to visit a museum, in which ancient artifacts showcased, though their chaperon becomes ill, and they are out of luck. They decide to have Curtis be their chaperon, so they shave him and give him modern clothes. While at the museum, Phil promises he'll go with Keely to investigate a forbidden room in which a mummy is being kept, though once he sees a piece to his time machine, he must retrieve it and blow off Keely.
Phil and Keely are hired to baby sit Mr. Messerschmitt’s nephew, Nathan, at Phil’s house, though his dad won’t be there to supervise. Phil promises not to use any futuristic gadgets to aid him in baby sitting, though Nathan proves too much for them to handle, so Phil discovers a loophole and has Keely use the WIZRD to make Nathan more mature, but she uses it too much and makes him like a grown man. While trying to reverse it, she accidentally hits Phil, so instead of making Nathan back to normal, she makes Phil believe he’s five years old.
Meanwhile, Pim makes volcanoes for the science fair which she attempts to sell to her peers who don’t want to make their own.
Phil solves a difficult math problem with ease due to the problem being “third grade stuff” in the future. If anyone solves the problem, the whole class will be granted no math homework for the rest of the year, so Keely tries to convince him to say the answer, though while convincing him, she talks too loudly and Mr. Hackett over-hears her recite the answer. She is taken into an advanced math class, in which Phil must continue to do her work, as if it is discovered that the work was too hard for her, Mr. Hackett will know that Phil gave her the answer, which could support his theory of them being aliens.
Meanwhile, Pim attempts to use massive static electricity to gain vengeance against the Fashion Zombies who humiliated her previously. She plans to use it to make their hair stand on end.
Pim decides to become principal for a day so she can finally gain a position of power. Soon, her power goes to her head, making everyone annoyed with her. Phil and Keely arrange a resistance, and attempt to overthrow Pim from her position, with the help of Mr. Hackett, whom she fired as vice principal, and Li’l Danny, whom she denied the position of vice principal.
After his room suffers some destruction, Phil is forced to move into the garage with Curtis. Curtis, finding Phil as an annoying room mate, jumps at the opportunity to move into Phil's room when it is fixed. When he says he wants to be treated like an adult, Lloyd takes him quite seriously, and even shuts off his power when he doesn't pay the electric bill. It is then when Phil realizes that perhaps being on his own isn't all he thought it would be.
Fed up of keeping his identity a secret, Phil finally tells Hackett, of all people, that he is from the future. Shortly after he tells this, the Timekeeper stops time, reminding Phil that doing what he just did was the worst thing a time-traveler could do. Phil refuses to take back his actions, and soon becomes the most popular kid at school. He thinks all is well until he realizes how distant from his best friend he has become.
Pim uses future technology to beat out the edge at a physical fitness competition, but soon learns that a quick fix isn't the best way to go.
Phil recalls the story of how he and Keely first met the previous Christmas, when Phil used the time machine to help save the Pickford Yuletide Star, which adorned the tree in town every year. Lloyd and Barb tell how they ended up getting the house they currently live in.
During a science project, Keely notices Grace, a popular pretty girl, looking at Grady, a sort of nerdy boy, with a look of liking. She wants to set them up, but Phil does not want to be a part of it. So Keely uses the instamorph and morphs into Phil to talk to Grady.
Keely scores a new broadcast schedule for her new tv show "Keely Teslow Investigates: I'm Keely Teslow", but no one ends up tuning into it. Scared that she might just lose her career as a reporter, Keely goes to the one person who's willing to help only for the benefit of herself: Pim.
Phil tries his best to give Keely the best birthday gift without use of future technology. Pim meets a new boy in class with similar interests.
The Diffy’s become ill from a future disease which alters their appearance to give them green skin and white, long beards. Each family member’s personality is also reversed, making Lloyd and Phil liars, Pim a kind, sweet-hearted person, and Barbara a savage. Phil’s inability to tell the truth makes him hated by everyone in H.G. Wells, and also causes Keely to go on a date with Bruno.
Phil loses his WIZRD, and Pim sees that Lil' Danny has found it while searching around the school with his metal detector. She obtains the WIZRD from him, though he steals it back from her once she's distracted, and gets it confiscated by Vice Principal Hackett. Phil and Keely are unsuccessul in retrieving the WIZRD, so they enlist the aid of Pim.
Phil meets a student at H.G. Wells that turns out to be his great-great-grandfather and almost alters his family's history.
It's nearing the end of Phil and Keely's sophomore year, and the yearbook results are in! Phil and Keely are voted "cutest couple", which surprises them, as they're not a couple in the first place. This causes them to finally spill their feelings for each other and become a couple. Troubles arise, though, as Pim accidentally fixes the Time Machine and the Diffys decide that it's finally time to go home. How will Phil say goodbye to Keely now, when their relationship has finally gone one step further? How will Keely react?