Mr. Burns withdraws a $1000 bill from an ATM, but he drops it and an updraft carries it away to the Simpsons' house, where it is found by Bart and Milhouse. Marge makes Bart and Homer put up fliers so that the person who lost the bill can reclaim it. No one can describe it correctly so Lisa suggests that they spend the money on a vacation, but then decide against it because Homer always manages to ruin any trip they go on. After realizing he can make money from the bill, Bart displays it in a museum in his tree house. Mr. Burns visits and reclaims his money, forcing Bart to close his museum. However, Bart has made over $3000 from the museum so they decide to spend the money on a vacation for Marge. Abraham Simpson suggests they go to Britain, where he hopes to meet his long-lost love Edwina. During World War II, he made love to her after claiming he was going out to the front lines the next day, not realising that he really was shipping out the next day (D-Day).
Upon their arrival in London the family is greeted by the Prime Minister, Tony Blair, whom Homer mistakes for Mr. Bean. They visit London's tourist attractions, and later meet J. K. Rowling and Ian McKellen. Grampa tries to contact Edwina whilst Bart and Lisa go on a "sugar rush" after discovering the joys of British candy. Homer and Marge rent a Mini Cooper and start to drive around London but get stuck on Hyde Park Corner. After literally driving in circles for hours, Homer decides to break out of it, plows straight through the gates of Buckingham Palace and slams into Queen Elizabeth II's horse-drawn carriage.
Homer is put on trial for causing harm to the Queen as well as wrecking her carriage. He humiliates himself by calling the Queen an impostor, since her luggage is inscribed "H.R.H." which he believes is short for "Henrietta R. Hippo", and mistaking the judge for a woman due to the wig he is wearing. The Queen, highly offended, demands that he be executed. He is taken away to the Tower of London to await his execution, where it is planned for his head to be stuck on a pike. The rest of the family call him from outside and Lisa tells him that he can use a secret tunnel that Sir Walter Raleigh built to escape. However, the tunnel leads straight into the Queen's bedroom, and she calls her guards. Homer pleads with the Queen to find it in her heart to forgive him and she allows him to leave the country on the condition that he take Madonna back to America with him. As they prepare to leave, Edwina appears and introduces Abe to her daughter Abbie Simpson, who looks and sounds like a British female version of Homer. Fearing that he is most likely the father, Abe runs away quickly to the plane.