Phineas and Ferb spend the morning watching a whodunit mystery marathon, the suspense intrigues Phineas and decides today, their going to make the greatest whodunit mystery ever. Phineas writes the script and Ferb builds the stage, Isabella, Baljeet and Buford come to see what they are doing. Phineas gives the kids roles in the play, Phineas is a kidnapped billionare, Ferb is the mysterious detective, Isabella is eager to accept the role of the missing billionare's lovesick maid, Buford becomes the aggresive bodyguard, and Baljeet becomes the nervous and insecure butler. The neighborhood comes and the show begins. The eccentric and and charming billionare Phineas Flynn returns home after work at Flynn Industries, a research and design center. He is greeted by his staff, Isabella the maid, Baljeet the butler, and Buford the bodyguard. Exhausted, Phineas goes to his bedroom, Phineas hears footsteps in the hallway, ignoring them Phineas proceeds. Phineas lies down, and a shadowy figure comes up behind him, hits him in the head with a bat, and drags him away. The staff hears the disturbance and goes to Phineas' room to find him gone. The next day, a newspaper falls at the door of famous detective Ferb Fletcher, he reads of Phineas' mysterious disappearance. Ferb arrives at Flynn manor, staff lets him in. Ferb first goes to Phineas' room. After exploration, Ferb finds in his desk Phineas' will. Astoundingly discovers Phineas' fortune was to be passed down to his staff. They respond by saying that they weren't just employee's to Phineas, they have been friends since high school. Ferb concludes that whoever the kidnapper is, he's after the Flynn fortune, and most likely the remaining employees will be his next target, for if they are missing the entire fortune will be passed down to the remaining heir. Phineas wakes up to find himself tied in a dark room, he knows that he has to get free and find out the identity of his kidnapper. Ferb asks to speak to Isabella, alone. Isabella nervously agrees. Ferb asks what kind of relationship did she have with Phineas in high school, Isabella tentatively says they were good friends and she had nothing against him. Ferb notices she momentarily glances at a closet. Ferb becomes suspicious and proceeds towards it, Isabella warns against it. Ferb discovers a shrine to Phineas, he asks Isabella to speak the whole story this time. Isabella confesses, she had had a crush on Phineas throughout high school, but she never told him because all the girls conviced her that Phineas was out of her league, she was always desperate to become rich so she would have a chance to get close to Phineas. Ferb formulates that Isabella would want to go to extreme measures to become in Phineas' league, suddenly a scream is heard, Ferb discovers that Isabella had gone missing as well. Meanwhile Phineas finally breaks out of his ropes and explores the abyss he was locked up in, Phineas thinks to himself that he's been betrayed by one of his closes friends. Ferb next interviews Baljeet, he says that back in high school he was a member of the science club, and he was dedicated to discover cold fusion, while most of the science club laughed at this idea, Phineas encouraged it, he said he could fund him once he's inherited his family's fortune. However, Baljeet eventually gave up his dreams. Ferb thought if Baljeet could inherit Phineas' fortune it would certainly give him enough funding to continue his experiments. However Baljeet goes missing as well. Phineas continues to traverse the dark room, as he wonders which of his friends has turned against him. Ferb finally moves on to Buford, he says that he was the football quaterback in high school, and was very popular, but ever since Phineas came along he's always been second best, however, him and Phineas soon become friends and begins to forgive Phineas even though he got all the attention. Ferb was not entirely convinced all had been forgiven. Ferb is baffled when Buford vanishes too. Phineas finally finds the way out and finds himself back in his room. Ferb finds him, Phineas asks if he's figured it out yet. Ferb regretfully says that evidence points that all three employees planned the kidnapping in a group effort, and that all three culprits have escaped. Phineas is shocked to find out that his closest friends have been scheming against him. Phineas hears frantic struggling on the other side of a bookcase. Phineas finds his friends tied up and gagged. After untying them, Phineas realizes Ferb has lied. Ferb admits that he was the one who kidnapped Phineas and the others all along. When Phineas asks why, Ferb says it was the only reason he was famous, he simply just commits a false crime, gets the dirt he needs, places the blame on someone else, and the news feeds on his "triumph". Although Baljeet wonders how Ferb kidnapped them even when he's not in the room. Ferb answers that he planted traps in different parts of the house that he can activate remotely, and those weren't the only ones. Ferb then activates ropes from the ceiling that bound Isabella, Baljeet and Buford. Ferb, makes a proposition for Phineas, either he go with him to the police to claim the staff kidnapped him, or he will tighten the ropes and strangle them. Phineas instead makes a better deal, he claims that he dissapeared on purpose so he could kidnap the heirs to his fortune, the fact that the culprit was the victim would make Ferb a legend. Ferb agrees, cuffs Phineas, and heads to the police station. While trying to find a way to get out, Baljeets panics and struggles, and his abnormally thin body slips through the ropes. He cuts the others down and they go after Phineas and Ferb. As they reach the police station, Isabella, Baljeet, Buford attack. Isabella fights off Ferb, while the others uncuff Phineas, when Phineas says that Isabella was amazing she blushes. Buford tackles Ferb, and claims that it was just like football. Finally Baljeet knocks Ferb unconcious when he shocks him with a cold fusion electrod, Phineas says that he thought he gave up cold fusion, and Baljeet says not before he finished. Phineas cuffs Ferb and take him to the police. Phineas narrates the epilogue, Isabella finally won Phineas' heart and they eventually got married and had a daughter named Julia. Phineas provided Baljeet enough funding to continue his experiments, and won the nobel prize. Phineas promotes Buford to his chairman in Flynn Industries, and appeared next to him on many magazine covers. Ferb was thrown in solitary, during his first day, the many people he framed recongnized him and beat him up. The audience applauds, and the cast takes a bow.