An old Vulcan woman is meditating. Her son Lorian enters and says that they were unable to prevent the Xindi weapon probe from entering the vortex and now it's on its way to Earth, just like something that happened before. The woman, who turns out to be an older T'Pol, tells him that he has no choice but to find Archer.
On Enterprise, Trip pretends he wants neropressure, but actually he just wants to make sure T'Pol is okay since she's been withdrawn lately. She says she's fine (also cancelling the sessions) but has an uncharacteristically nervous expression. Enterprise is nearing a nebula that will take them to a rendezvous with Degra near the Xindi planet. Degra had warned them that there were one or two hostile Kovaalan ships in the nebula, but when they arrive, they find at least six ships. They begin using a Metreon cloud to hide their signature.
Degra's ship is locked with a Xindi-Primate ship for a meeting between three council members. The Xindi-Primate he's working with is angry that he told the humans where the meeting place was. Degra points out that the Enterprise is the only ship in the Delphic Expanse and is heavily damaged. The three Xindi councilors discuss whether it's a good idea to let Archer know about the meeting, but Degra maintains that it's worth the risk, adding that they'll need to protect the Enterprise from the reptillians.
Enterprise drops out of warp near the nebula and finds a ship which they think is the Columbia, but it has Enterprise's markings and is captained by a man named Lorian, who asks Archer to reverse his course. Archer complies, and meets with the ship's crew. Lorian explains that Enterprise entered the nebula, was attacked by Kovaalans, escaped them by reaching the subspace corridor, but accidentally destroyed the corridor when the impulse manifold created a "particle wake". This sent them back in time and thus, Enterprise became a generational ship. Lorian then reveals that T'Pol is his mom.
Lorian advises Archer not to enter the corridor, but instead to enhance the plasma injectors using Haradin technology. Lorian couldn't do that himself, since his injectors are worn down, but it could be pulled off with new injectors and structural changes to Archer's ship. Phlox does a DNA test, determining that Lorian is telling the truth, that his dad is Trip, and that the executive officer, Karyn Archer, is Archer's great-granddaughter.
Trip, who, as it turns out, died when Lorian was fourteen, instantly forms a bond with Lorian. Meanwhile, Karyn takes Archer on a tour of the ship and explains that Phlox had nine kids with Amanda Cole (hence the high amount of part-Denobulan kids). She then explains that her great-grandmother was an Ikaaran named Esilia who Archer married after rescuing her ship. Archer notes that this explains why the Xindi kept asking how many human ships were in the Expanse. He is taken to the quarters of T'Pol, the only living member of the original crew, who is much more expressive in her old age. She's curious about Trip, but would find actually talking to him too awkward. She then gives him a PADD that proves that Lorian's plan could result in Enterprise's destruction.
In the mess hall, Hoshi reveals to Travis that she has two kids named Toru (boy) and Yoshiko (girl), but didn't want to know who their dad was. Travis reveals that he married Corporal McKensie, and Malcolm awkwardly reveals that he remained single. The ensigns leave and Malcolm begins hitting on a woman. Meanwhile, T'Pol tells Archer that she and Trip agree with the elder T'Pol— Lorian's plan could easily overload the injectors and destroy the ship. The elder T'Pol shares a new plan— modify the impulse manifolds so the corridor won't be displaced. Archer then tells Lorian off for thinking up such a risky plan without warning them of the dangers and refuses to execute his plan.
Lorian berates the elder T'Pol for warning Archer, worrying that the events will all happen again, but she thinks that he just feels guilty about failing to stop the Xindi probe, which makes him angry. He meets up with Karyn and Greer, the tactical officer, to outline his plan to steal the injectors and warp to the meeting place.
While Trip and the younger T'Pol work on the modifications, he goes on about the alternate timeline in which they marry, but she doesn't seem interested. When he mentions that they could develop romantic feelings, she becomes annoyed and regrets having sex with him. Lorian attempts to steal the plasma injectors, but is caught by Trip. Trip tries to get Lorian not to do it, but Lorian stuns him with a phase pistol.
On the bridge, Archer is informed that the warp engines and plasma injectors are down. Engineering doesn't respond, and the alternate Enterprise undocks and doesn't reply to hails. Archer orders Malcolm to disable their engines, which he does, then Lorian orders a retreat and for Greer to return fire. Archer orders T'Pol to the transporter room, and when Greer returns fire, the Enterprise loses hull plating and weapons. T'Pol beams an EPS manifold off Lorian's ship, then Archer orders her to take the primary relays from C-Deck, which causes Lorian's ship to lose power.
Archer hails Lorian (with Malcolm warning him that Lorian has a torpedo) and emphasises to him how many people would be harmed if he pulls the trigger. Karyn also insists on stopping the fight, which finally causes Lorian to surrender.
In the brig, Archer tells Lorian that he was lucky that everyone's injuries were minor, but adds that his (Archer's) ship was almost crippled. Lorian still insists that his plan is the only logical one that has a chance of success, and that Archer's mission is already over. Lorian reveals that he feels terribly guilty for not destroying the Xindi probe, but Archer assures him that his (Archer's) plan is the safest and decides to free Lorian so they can work together.
In the elder T'Pol's quarters, she tells the younger one how to use "isomagnetic collectors" (pieces of Ikaaran technology) to reduce the particle wake and warns her that the effects of the Trellium-D addiction will never go away completely, suggesting that she get together with Trip.
Enterprise approaches the nebula and is fired at by Kovaalans. Malcolm is unable to return fire, so Archer hails Lorian. Both Enterprises attack and disable the lead ship, prompting the other two to retreat. Enterprise is now unable to move due to a busted drive coil, so Lorian's Enterprise tows it with a tractor beam. Four more Kovaalan ships appear and fire at the aft plating, which fails, as do the weapons. Lorian releases Archer's Enterprise towards the corridor, and they emerge, but Lorian doesn't (it's unknown if he died or was erased from existence). Just then, Degra appears, noting that Archer is early.
Tropes in this episode include:
- Actually Pretty Funny: Lorian cracks a smile when Trip comments that his ears obviously came from his mother.
- Ambiguous Situation: Lorian never emerges from the nebula, and it's unknown if that means he and his crew were killed by the Kovaalans or vanished due to history changing. T'Pol thinks it's the former since she and the others can still remember the alternate history, but it's ultimately left unclear.
- Alone Among the Couples: Reed is rather distressed to discover his alternate self was the only one of the main cast not to get married. As Hoshi points out, since only a third of the crew are female, about half of all heterosexual male crew members will end up alone.
- Antagonistic Offspring: Lorian, son of Trip and T'Pol, stuns his father to steal the antimatter injectors.
- Apologetic Attacker: Lorian apologizes to Trip before stunning him.
- Call-Back: Throughout the season, the Xindi wonder how many human ships are in the Expanse. Degra even tells Jannar "those readings were never confirmed." Turns out, they were right.
- Combat Pragmatist: Outgunned, Archer resorts to using the transporter to beam away the alternate Enterprise's power systems.
- Fearful Symmetry: Enterprise vs Enterprise. As T'Pol points out, the two ships are pretty much evenly matched.
- Foreshadowing: Early on, Degra and Jannar discuss "never confirmed" sensor readings suggesting the presence of other human ships in the Expanse. Later in the episode, we learn that this is because they've been picking up the presence of the future Enterprise all along, but that the future crew have been carefully avoiding direct encounters. (As it turns out, this is also why, back in "Azati Prime", Dolim demanded that Archer tell him how many Earth vessels had entered the Expanse; the Xindi had reason to believe there were others out there.)
- Half-Human Hybrid:
- Lorian is the son of Trip (a human) and T'Pol (a Vulcan).
- Phlox (a Denobulan) had nine kids with Amanda (a human), leading to many part-Denobulans on the crew.
- Karyn is an eighth-human hybrid— she's the great-granddaughter of Archer (a human) and Esilia (an Ikaaran).
- Heroic Sacrifice: The alternate NX-01 stays behind to cover Enterprise into the subspace corridor. Whether they were destroyed or the successful trip negated their existence is anyone's guess.
- Hypocrite: Archer criticizes Lorian for his theft of Enterprise technology, only two episodes after Archer did the same to another ship.
- Interspecies Romance: In the alternate timeline, Archer ended up marrying an Ikaaran.
- Massive Numbered Siblings: Phlox and Amanda ended up having nine children together, and Phlox already has five, meaning that in the alternate timeline, he ended up with fourteen kids total.
- My Greatest Failure: Lorian failed to stop the Xindi when he had the chance.
- Negative Space Wedgie: Of course a Delphic Expanse wormhole would send the alternate Enterprise back in time. It's not even the most bizarre thing that's happened in the Delphic Expanse.
- No Time to Explain: Lorian, when he first tells Archer to reverse course away from the nebula.
- Our Wormholes Are Different: This one gives Enterprise the Timey-Wimey Ball the first time through.
- Ramming Always Works: Lorian's last-ditch plan to stop the probe, except that he hesitated to carry it out.
- Rescue Romance: Heavily Implied by Karyn when she tells Archer that his future wife is someone who he rescues from an anomaly field.
- Theme Naming: It's revealed that the NX-02 was named Columbia. The novels confirmed that all of the NX-class were named for America's space shuttles.
- Time-Travel Tense Trouble: Phlox experiences this when telling Archer how, according to Lorian, he discovered—or will discover—a way to combine human and Vulcan DNA.
- The Unreveal:
- Hoshi learns that she had two children on the alternate NX-01, but she chooses not to find out who the father was.
- The fate of the alternate Enterprise is never revealed.
- Villain Has a Point: Mallora reasonably points out that the humans could have manufactured their "evidence."
- Well-Intentioned Extremist: Lorian understands the importance of making the rendezvous with Degra, even if it means fighting his own ancestors.
- Whole-Plot Reference: It takes a similar premise DS9's "Children of Time" in that both involve characters meeting their alternate descendants. However, the ethical issue of the descendants' lives being negated isn't raised (since they don't want the alternate timeline to happen anyway) and it instead focuses on which plan to take for escaping the anomaly.
