The O'Brien family, reunited after Deep Space Nine has been reclaimed, takes a family trip to planet Golana IV. While playing, eight-year-old Molly (Hana Hatae) falls into an abandoned time portal despite Miles's (Colm Meaney) efforts to save her; the portal closes after Molly passes through. The station's staff quickly comes to the O'Briens' help to try to recover Molly, using transporter technology to lock onto her signal once they are able to open the portal again. However, they find the portal has opened at a different time, and the Molly they rescue is now 18 years old and feral after having to survive on her own for the last ten years in the planet's past. Molly is brought back to the station, and placed in a special habitat made to resemble the planet, to allow the O'Briens to try to reconnect with their daughter. During this time, Jadzia Dax (Terry Farrell) offers to look after infant Yoshi O'Brien, but when this interrupts her planned scientific ventures, Worf (Michael Dorn) offers to watch the child.
Molly slowly comes to remember her parents, but still is barely controllable and confined to the boundaries of the habitat. The O'Briens take her to a holosuite to give her the appearance of more space, to which she responds positively. However, when two Klingons demand the scheduled use of the holosuite, Molly becomes violent. Starfleet informs the O'Briens that it plans to put Molly into a mental institution, a situation that neither Miles nor Keiko (Rosalind Chao) believe is ideal for Molly. With help from a sympathetic Odo (René Auberjonois), Miles works to secretly return Molly to the portal on Golana IV, with the intention of destroying it to prevent Starfleet from finding her. After Miles and Keiko say their goodbyes, Molly returns through the portal but encounters her younger self, only a short time after she had fallen through. The older Molly points her younger self back through the portal; as soon as the younger Molly passes through, the older Molly disappears. Molly reappears moments before Miles is about to destroy the portal, and the family happily reunites. Back aboard the station, they find that while Worf had a difficult time caring for Yoshi, the infant manages to learn one of the Klingon games Worf taught him, making Worf proud of himself.