As Neelix presses Janeway for information about Earth's history, she reminisces about one of her ancestors, Shannon O'Donnell. Shannon was in Indiana in December of 2000 when she discovered a quaint downtown area about to be destroyed and replaced by the Millennium Gate. The world's first self-sustaining civic environment, the Gate had developers offering Henry Janeway a lot of money for his bookstore, but he wouldn't sell. Through a chance encounter when her car broke down, Shannon and Henry began working together to prevent the destruction of downtown Portage Creek.

A database search uncovers a picture of Shannon and her children, which Janeway wants to frame. She explains that she grew up admiring Shannon and her bravery in building the Millennium Gate, which became the model for the first habitat on Mars. Back in 2000, Shannon is approached by Gerald Moss, one of the developers who knows her from her days of astronaut training at NASA. Knowing that Shannon recently lost her job, Moss tries to lure her to his team as consulting engineer in return for Shannon convincing Henry to give up his shop to the project.

Intrigued by the experimental biosphere, Shannon tries to talk Henry into seeing the benefits of the Gate. He will hear nothing of it, however, and Shannon leaves when the two of them begin fighting. On Voyager, the crew trades stories of their family history. When Janeway asserts that Shannon did work on all the early Mars projects, Paris contradicts her. He is an expert on that subject, and he is positive there was no O'Donnell working on those projects.

Further research shows Shannon did not overcome any great obstacles to build the Millennium Gate, as Janeway had believed. She was only a consulting engineer, and the sole opposition she faced was Henry, who became her husband. As Shannon prepares to leave town, and the Gate developers are about to move their plans to another city, she suddenly returns to Portage Creek to talk to Henry.

Shannon reveals she has come back to be with Henry. She wants to explore the future, but he must be willing to leave the past behind. With only a minute to spare until midnight of New Year's Eve and the deadline for the Millennium Gate project, Henry agrees to rebuild his shop in the new biosphere. Janeway is disappointed Shannon was not the courageous explorer she always believed her to be, but she has no idea what her ancestor did for the town of Portage Creek, and a man scared to face the inevitable future.