Phineas and Jeffrey journey back to 1924 Hollywood to convince Franklin D. Roosevelt to give up on a career as a film director and go into politics instead.
In order for the future American Space Program to succeed, the Voyagers must go back to Austria just after the end of World War II and prevent rocket scientist Werner Von Braun from being captured by the Soviets.
Phineas and Jeffrey assist a fellow Voyager who is trying to recover the stolen Mona Lisa from a thief aboard the doomed ocean liner Titanic. Then in 1884 France, Jeffrey is bitten by a rabid dog and his only chance of survival is treatment with a new vaccine invented by Louis Pasteur.
Arriving at Pearl Harbor on 6 December 1941, the Voyagers try to warn General MacArthur about the upcoming Japanese attack. Then then end up in 1860's Utah to help a young Buffalo Bill Cody with the Pony Express mail service.
First, the Voyagers help Albert Schweitzer in his efforts to bring medical aid to a dying African tribal chief. Then they arrive in 1887 to help Annie Oakley, who is with Buffalo Bill's circus that is in England to perform for Queen Victoria.
The Voyagers must go back in time to before the American Revolution to make sure that George Washington joins the American rebels rather than the British. Then in 1892 they help early union leader Samuel Gompers, and Jeffrey gets to meet his great grandfather, a lawyer helping the labor cause.
The Voyagers encourage Lindburgh on the eve of his trans-atlantic flight, then help Robin Hood sneak into an archery competition to rescue Maid Marian.
Jeffrey and Bogg talk the pirate, Jean Lafitte, into leaving the beautiful Bahamas for New Orleans where General Jackson is going to need his help against the Red Coats.
On their way to rescue President Lincoln, who has been kidnapped by Confederate soldiers, the Voyagers are briefly diverted to 1832 London where they encounter young author Charles Dickens.