As Springfield celebrates its bicentennial, Lisa's class at Springfield Elementary School are assigned essays. Lisa goes to the historical society to research Jebediah Springfield, the founder of Springfield. While trying to play Jebediah Springfield's fife, she makes the shocking discovery that the town's founder was actually a villainous pirate and enemy of George Washington who kept his dark past hidden. He had written his confession on the back side of a portrait of Washington and hidden it in his fife. Meanwhile, upon Lisa's suggestion, Homer is elected the town crier after he demonstrated that he was better suited to the position than Ned Flanders.
Lisa conducts further research about Jebediah Springfield, and finds out that he once lost his tongue to a Turk in a groghouse fight and had it replaced with a prosthetic silver tongue. The town, including Marge, does not agree with Lisa's revelations, resulting in an "F" on a report about Springfield while Ms. Hoover deems her to be a "PC Thug." Homer believes her, and sympathizes with her story, claiming he's been called a "greasy thug" too. However, when Lisa attempts to show the town historian Horace Hurlbut the confession, he dismisses it as an obvious forgery, and when she presses him, he bans her and her descendants from the museum for three months. Lisa tries to convince the town her claims are true, but is met with outright hostility everywhere. However, she convinces the municipal government to disinter Mr. Springfield's body to search for evidence of a legendary silver tongue. Despite Lisa's suspicions, when they open the coffin, the skeleton possesses no silver tongue. Lisa is forced into admitting she was wrong and Mayor Quimby strips Homer of the role of town crier and reassigns it to Flanders.
That night, Lisa has a dream wherein the ghosts of Jebediah Springfield and George Washington appear. After seeing the incomplete portrait of George Washington in her classroom, Lisa soon figures out that the piece of paper upon which the confession is written is the bottom half of the portrait. She confronts Hurlbut with this piece of evidence. Hurlbut confesses that he stole the tongue while the dust cleared seconds after the coffin was opened and hid it in a cowboy maquette in the museum. He explained that he had done so to protect his career and the myth of Jebediah Springfield. After realizing the mistake of celebrating a pirate, the two decide to go public with their discovery. Just as Lisa is about to expose the "real Jebediah" to the parading townspeople, she realizes that Jebediah Springfield's good image means too much to the town, and decides to keep the truth a secret, knowing they will lose hope and morale if the truth is revealed to the public. At the parade, Homer takes a tricorne and bell from Flanders and replaces him, marching through the parade with Lisa on his shoulder.