Stewie and Brian are watching Stewie's favorite show, called "The Cadwalliders of Essex" (a parody of Downton Abbey). Meanwhile, Peter and Chris play a game called "Unga Bunga", where they try to knock each other down using mattresses. This ultimately results in Chris hitting, knocking down and breaking the TV Stewie is watching. Fed up with Peter and Chris after their horseplay destroys the TV, he throws a temper tantrum. Later when Lois tries to comfort Stewie, he bites her right thumb and throws a framed picture of Meg against a door. Meg enters the living room and tries to give Stewie a hug only for Stewie to break her nose by headbutting it, and then Lois puts Stewie in his room for a time-out for everything he did until he learns to behave again.
The next day, Stewie reveals that he has built a new time machine and uses it to stop his conception. Going back three years into the past, he observes the events prior to his conception, like Peter having his own public access show and Lois improvising some lyrics in the theme song in Stewie's place. Getting back to business, he discovers that Peter and Lois were truly in love but sets out to ruin things. Money fails to work so he shaves Peter's hair to get them to argue, but Lois flatters Peter, thinking that he can pass off as a celebrity. Peter even claimed that he was Bruce Willis. But he finally succeeds when he gives Peter's porn collection to Goodwill and writes "Vile Woman" on the wall. This causes Peter to leave Lois and as a result, Stewie fades from existence, but is reborn into a wealthy British family.
Things seem like fun at first, but Stewie's new older brothers Jaidan and Aidan give him a hard time and he discovers they are not as foolish as his old family. He is dumped off to be raised by staff consisting of Nigel the butler, some maids and other assorted servants. Later that night, Stewie realizes he misses his old family because he was the smart one. Upon finding a dueling pistol in his bed, he accidentally shoots it, where the bullet knocks the bow off the cat belonging to the baby (referred to in the episode's press release as "Cousin Earl") upstairs, who vows to duel Stewie. His new father is a professor at Oxford University and he sets out there to use the lab to build a new time machine. Piecing together a rudimentary machine, he is almost caught by the British Father but gets away.
Stewie meets his past self and tells him about his bad alternate life and together they stop the fighting by reminding Peter & Lois of how much they love each other by leaving Peter's "I Love You" picture to Lois in the refrigerator. They patch things up as Stewie says his goodbyes to his other self as a stage light falls on the British version who then fades away.
Returning to the original timeline, he is happy to be back as Cousin Earl shows up and shoots him in the arm. Chris reveals that he has spent three years reading Peter's porn collection.