Voyagers!

Jeff and Bogg arrive in 1930's New York and meet a retired adventurer/voyager, Isaac Wolfstein. They drop him off on an island to live out the rest of his life, save Albert Einstein, then pop back to Marco Polo's time...but Polo isn't where he's supposed to be. The two try to restore history but Jeffrey is caught by soldiers who plan to sell him as a slave. Bogg goes to Wolfstein to get advice, and just manages to save him from a nuclear test on the island. The two men return to save Jeffrey, then head off to lunch with Einstein.