This episode begins with Jimmy talking about Foucault's pendulum experiment for a school history report. Jimmy demonstrates with a simple model of the experiment with a tiny pendulum and a series of dominoes. Eventually one gets knocked over. Sheen remarks that the event is "cool" and asks when it will happen again. Jimmy responds, "In exactly one hour." Tired of waiting, Ms. Fowl bangs a gong to end his report.
Now Nick Dean comes up to tell a scary story about a salami-legged Phantom of Retroland, saying kids from an all-night swim meet take a shortcut through Retroland amusement park to return home and are faced by the Phantom. Jimmy wants to disprove Nick, so he volunteers to go to Retroland with Carl and Sheen.
Jimmy uses a hologram projector to give the illusion of him asleep as he sneaks out and catches Carl trying to escape from what is about to happen.
Upon arriving at Retroland, Jimmy uses an "Oxidation Accelerator" to break through the fence around the amusement park. As they arrive, it is midnight. The Phantom does not show up, so Jimmy decides to leave. As they do, Carl smells salami. In a moment, the Phantom approaches. The trio runs to a ride and go inside. The ride is then started.
Jimmy realizes the ride is a giant pendulum and decides to reperform Foucault's experiment on the ride itself. In a matter of seconds, the phantom is knocked down. When the ride stops, Jimmy, Carl, and Sheen get off to realize that Nick is the phantom in disguise. Now a second phantom appears, but Goddard, who came along, reveals the phantom as Cindy Vortex and her friend Libby Folfax.
Now another Phantom comes as soon as they leave. Jimmy rips off the coat of the Phantom to discover a pitch-black body. Believing that they have discovered the real phantom, the gang runs away. As Carl asks, "What about science?", Jimmy says: "Science, schmience; run for your lives!"
Meanwhile, that Phantom takes off his mask to reveal Jimmy's mother, Judy. This was to teach Jimmy a lesson about sneaking out.