Twin sisters Liv and Maddie finally reunite when Liv returns home to Wisconsin after starring for four years in a hit musical television show in Hollywood. The Rooney sisters quickly realize their polar opposite personalities put their unbreakable twin bond to the test. While their parents play referee between Liv, a cool, confident, social butterfly who loves to sing, and Maddie, a smart, athletic, high school basketball star who opts for high tops over high heels, brothers Joey and Parker seize the opportunity to capitalize on the chaos and get away with as much as they can.
Maddie is named captain of the girls' basketball team just as the school principal announces he is cutting funding for the program. Determined to change his mind, Maddie voices her concern to the principal, only to realize her team has abandoned her. Frustrated with her lack of leadership skills, Maddie turns to Liv to help her earn the team's respect. Meanwhile, Parker and Joey are challenged trying to find a bevy of tarantulas that escaped after Parker brought them home from school unbeknownst to their mom.
After Liv realizes just how much Parker has grown up while she was away, she volunteers to supervise his sleepover in hopes of reconnecting with him. But when all her activities backfire and start to embarrass Parker in front of his friends, Liv has to up her game in order to impress her little brother. Meanwhile, Maddie and Willow work on a school project, and Joey and Pete go on a road trip to the Pastrami Palace that leads to a wild night of fun.
When Joey is too nervous to talk to the new girl who he likes, Maddie decides the best place for him to practice talking to girls is at the high school dance–when everyone is in costume. Meanwhile, Parker booby-traps the house to protect one of the family’s most prized Halloween decorations from being stolen.
Liv wants to back out of being a celebrity judge at a skateboarding competition after her boyfriend, a skateboarding pro in town for the competition, breaks up with her via text. Meanwhile, Joey and Parker are ecstatic when they meet a masked skateboarding pro who is famous for his massive wipeouts.
Ridgewood High is hosting the annual "Brain Olympics", and Joey is intent on forming a team in hopes of winning. Liv, in an effort to shed part of her girly image, convinces Joey to let her join the team. In competition, each team has to build a Rube Goldberg machine, but when Joey thinks she is not clever enough, Liv decides to build her own. Meanwhile, Maddie holds a yard sale to raise funds for the French Club's trip to Montreal, and a priceless childhood memory accidentally gets sold.
The annual Stevens Point Holiday Spectacular is coming up, and Liv is asked to host the televised event. When Liv discovers the little girl she's asked to perform with shares the same strong desire for the spotlight, trouble ensues. Additionally, Pete and Maddie are in charge of decorating the city's Christmas tree, but the power goes out amid Liv's performance. Meanwhile, Parker swindles money from Joey while dressed as Santa and an elf in order to purchase an expensive present he suspects no one will gift him.
When Maddie fails her driving test and Liv needs help trying to get a part in a sci-fi play, they decide to switch so Liv takes Maddie's driving test and Maddie auditions for Liv. But when Maddie accidentally yells, "Bam! What!?" Joey and Parker realize it's her and not really Liv, and Liv wrecks the car during Maddie's driving test.
Maddie is anxiously awaiting the arrival of a letter from the Junior Olympics that will tell her if she's been invited to try out for the basketball team. When the letter comes, Liv is worried about Maddie leaving because it was the same way when Liv left for Hollywood and they end up going into a flashback on the day Liv left for Hollywood.
While Joey and Maddie try to catch Diggie before he departs for Australia, Liv covers for Maddie at home. But when Diggie shows up at the Rooney house, chaos ensues, reminding Parker of his favorite soap opera drama. Liv gets a call from her manager telling her she landed a coveted role in a new TV show "Voltage".
Liv, Maddie and the rest of the Rooney family are excited to start their new life in California. As the school year begins, the Rooney's cousin, Ruby, returns home from a summer trip. Excited to have "sort of" siblings, Ruby can't wait to finally be a sister but finds herself in the middle of a sister-fight between Liv and Maddie. Meanwhile, Joey and Parker attend their new Science and technology school and their experience is not what they expected.
Liv and her fellow female co-stars of "Sing It Louder!!" attempt to break the stereotype that boys are better than girls at 'boy stuff' by organizing a woodblock derby race against the boys. Meanwhile, Maddie and Willow take part in a challenge at their local restaurant which has only been won by men before.