A team of Starfleet scientists are on the case, and Dax explains that the device is a Portal to the Past built by an extinct species. Molly's been sent 300 years in the past, when the planet was uninhabited. With some science magic, they reactivate the device and beam Molly out, but instead of the cute 8-year-old they know, they pull out a feral adult woman, who promptly goes nuts and needs to be sedated. It seems they pulled Molly out too late, and she's spent years living on the planet by herself.
The O'Briens bring Molly back to a park they build in the station's cargo bay and work on resocializing her. She is afraid of them and only dimly remember a smattering of language, so progress is slow. She recognizes her old doll, Lupi, and begins to speak a few words. She even draws a crude picture of herself and her parents at the picnic. When she asks for "home," the O'Briens take her to their quarters, but she's insistent on returning to Golana, which she now sees as her home. Instead, they take her to a holosuite, where she exults in returning to the wild, but the family's purchased time quickly runs out. When O'Brien ends the program, Molly freaks out and rampages through Quark's bar, stabbing a patron.
While the O'Briens have been dealing with this, Worf has insisted on babysitting the family's youngest child Yoshi. Dax forces him to admit that he's doing it to prove to her that he can be a good father to their future children. Though exhausted, Worf rises to the challenge and begins teaching Yoshi some Klingon warrior games. One evening, however, Yoshi bumps his head while playing, and the ashamed Worf apologizes for failing to prove himself.
Molly is thrown in the brig, and Sisko tells O'Brien that Molly will likely be taken to a medical facility for long-term care, something O'Brien knows will not help her. The parents decide that the best thing for her is to break her out of the brig and return her to Golana, 300 years in the past, where she can live by herself in peace. They anesthetize the brig guard and carry her to a runabout but get caught by security. Odo allows himself to be persuaded to let them go, and they make it to Golana.
On the planet, the parents give Molly some survival tools and her doll Lupi, then tearfully bid her farewell. She steps through the reactivated portal and returns to Golana, but the adult Molly discovers the 8-year-old version of herself hiding in the cave. As O'Brien prepares to destroy the portal, the adult Molly gives Lupi to her younger self and sends her back through the portal, sending her "home." In the process, the adult Molly ceases to exist.
Back on the station. The O'Briens are overjoyed to have their child back. They thankfully take back Yoshi, not even acknowledging the bump on his head. Worf is happy to learn that his "Klingon warrior rituals" have made an impression on the child. As Molly settles back into her old life, she asks if she's going to see the woman who sent her back through the portal, and Keiko says that it will be a long time before she does. The little girl draws a picture of the picnic that strongly resembles the one her older version drew, giving the O'Briens pause, but they assure her that it's lovely.
Tropes
- Baby Fever Trigger: Worf and Dax have to babysit the O'Briens' baby son Yoshi while his parents are dealing with his time-travelling older sister Molly. Babysitting Yoshi makes Worf decide he wants kids of his own, and he feels he must prove himself able to take care of a baby.
- Baby Talk: It's apparently a Klingon hand-eye exercise to shake a rattle and go "Gung, gung, gung!" When Yoshi repeats the phrase later, Worf takes that as a sign that he's made an impression on the boy.
- Bar Brawl: Molly attacks Quark and his patrons, smashing furniture and bottles, until she is stunned by security.
- Bittersweet Ending: The O'Briens getting their daughter back at the end is certainly happy, but it's tempered by the fact her adult self ceases to exist because of the resulting paradox. The scene at the end where young Molly draws the exact same picture she drew as an adult is particularly heart-wrenching.
- Call-Back: Chester, Bilby's cat, makes an appearance in the O'Brien's quarters.
- Chekhov's Gun:
- Molly puts on a bracelet when getting ready for the picnic, and it helps identify the older version of her.
- Of less significance, but still bittersweet: when the O'Briens are first on Golana, little Molly eagerly demonstrates for her parents how she can cartwheel. Later, when they are using the holodeck to help her older self "go home", she demonstrates she has learned to do so very well over the last ten years.
- Continuity Nod: When O'Brien proposes using the portal again to try and retrieve Molly from just after she disappeared, Bashir sounds... a little strained as he explains that doing so would Ret-Gone the adult version. Now, why would Bashir have a problem with parents wanting to erase the difficult child they're got in favour of a "better" one?
- Do Wrong, Right: After Odo catches O'Brien and company at the airlock, he tells the chief he's disappointed... because Odo thought if anyone could break someone out of a holding cell and sneak them off the station undetected, it would be O'Brien. He then opens the airlock and lets them go.
- Dramatic Irony: As the adult Molly prepares to send the child Molly back through the portal, neither realize that O'Brien is about to destroy the portal. O'Brien readies his phaser while Molly pauses to rummage through her backpack for a doll.
- Easily Forgiven: There's no tension at the end of the episode that the O'Briens will suffer any consequences for knocking out a guard and stealing a runabout.
- Five-Second Foreshadowing: O'Brien insists to Molly that he won't send her away anymore and they'll never be separated again. What happens only a short time later? And with a vengeance, since it ends up being for ten years from her point of view rather than just a day.
- Forgotten Phlebotinum: If the main characters had remembered they have access to a reliable time machine they've used twice already, or the "Slingshot-around-the-sun" trick used by the TOS crew several times, the whole plot of this episode could've been avoided. Justified in they still need to know precisely when Molly was transported to for them to get her back.
- Spin-off material has also established that temporal displacement leaves the traveller molecularly out of sync with their new time, with the result that the only way such travellers can return is to re-use the original method; exactly what would happen if they tried to travel in another manner is unclear, but it's generally agreed it would be unpleasant at best.
- Grandfather Paradox: The adult Molly who finds little Molly never exists if little Molly did not stay in the past. Sure enough, once little Molly goes back through the portal, adult Molly disappears.
- Grievous Bottley Harm: Molly stabs an alien in the stomach with a broken bottle.
- My Future Self and Me: Little Molly thinks the woman who found her, the grown up version of Molly, is "so nice".
- Noodle Incident: Apparently, Worf has fought Kelvans at some point. Presumably that deal Kirk made with them didn't work out so well.
- Nubile Savage: Molly, returned from the portal.
- Picnic Episode: Molly was so excited to go on a picnic.
- Portal to the Past: The portal left behind in the cave.
- Precision F-Strike: When a failure to repair the time portal causes an energy surge, O'Brien exclaims "Bollocks!" in response.
- Reset Button: The O'Briens get eight-year-old Molly back safe and sound at the end.
- Ret-Gone: Adult Molly saving young Molly causes her to erase herself from existence.
- Serious Business: Worf is dead-set on proving himself worthy to Jadzia of being a good father to her eventual children by taking care of Yoshi. When Yoshi gets a boo-boo while roughhousing with Worf, it's a massive blow to his self-esteem and feeling of worth.
- Set Right What Once Went Wrong: 18 year old Molly sends little Molly back through the time portal.
- Wild Child: Molly lives alone for 10 years and returns without social skills or language.
- Year Inside, Hour Outside: Molly ages 10 years in the one day it takes to repair the time portal.
