Deborah slowly discovers that Dan may not be the thrilling inventor he claimed to be back in 1776, and questions their budding relationship. To get her back, Dan resorts to desperate (and alarming) measures. Meanwhile, Chris is under intense scrutiny from his mentor, Dr. Cobell, as he works to finally achieve tenure at the university.

In need of a victory, the trio heads back to the 1990s to give Dan another shot at his childhood dream: finishing the infamous "Bellybuster" ice cream sundae at a local parlor. As Deb bonds with the parlor's owner, Chris is on a mission to save a life in honor of his late British friend. But all of their plans are derailed when Dan runs into the bully that tormented him.

In need of some quick cash for Deb to purchase an ice cream parlor, the trio decides to make some money rather than save the world. But after Chris devises a strategy to cash in on the fixed 1919 Chicago World Series baseball game, their get-rich-quick scheme is derailed when they run into the infamous mobster Al Capone.

Dan, Deb and Chris find themselves stuck in 1920s Chicago, with Al Capone holding their time travel bag hostage. Chris opts for a play-it-safe plan, using history to take out Capone, while Dan and Deb befriend him instead. As they teach him how to be a better mobster - and husband - they quickly realize that proving their loyalty may not be as easy as they thought.

With the ever-present threat of losing tenure looming over him, Chris reaches out to John Hancock and Samuel Adams to help spice things up in the classroom in 2017. Meanwhile, Deb's dream of re-opening Chadwick's ice cream parlor is finally coming to fruition, but Dan has a few marketing ideas of his own.

Just as they're heading back to colonial times, John Hancock and Sam Adams meet the woman of their dreams and decide that there's no better way to determine who gets to court her than a classic duel. In the meantime, in hopes of garnering good publicity for Chadwick's, Dan sets up a meeting with a local reporter, who winds up asking some challenging questions about Deborah's identity.

Chris' life is in shambles, so Dan plays the time travel card with Dr. Cobell to help get Chris' job back, but his efforts go awry when he accidentally gives him a heart attack instead. Meanwhile, Deb hunts down Hancock and Adams to convince them to return to the past.