Flynn travels to 1931 Chicago to partner with gangster Al Capone. Lucy, Wyatt and Rufus, meanwhile, team up with the only man who can bring Capone down: federal law-enforcement agent Eliot Ness.

With one of our heroes' lives on the line, the team chases Flynn to 1954 through the paranoid corridors of Joe McCarthy's Washington D.C., en route to a secret, once-a-generation meeting of Rittenhouse leaders. While there, Lucy must wager the ultimate sacrifice to save history as we know it.