Eric, Dominique, Ajay, and Josephine are at home getting ready for a normal school day after two successful time-travel adventures. But the day might not turn out to be so normal after all! The kids' parents remind them that today is Coronation Day, and when they get to school, they find the Pledge of Allegiance replaced with an Oath to the King. Clearly, something is amiss, and the only way to fix it is to return to the Smithsonian, this time to the National Museum of American History. Their problems don't end there: the museum's famed American Presidency exhibition has been replaced with one on America's monarchs, complete with a portrait of George Washington being crowned as the first king! Enlisting the help of Gilbert Stuart, John Trumbull, and Thomas Jefferson and using their American history smarts, our heroes must try to thwart this wicked plot to change history.