Phlox tells Archer that Trip is in a coma, but he can make a clone of him (that will grow fast and live for about fifteen days) using a larva, that he can harvest neural tissue that Trip needs from. Archer is reluctant, but allows that procedure to happen, and the clone is made as a baby, who Phlox names Sim and raises in sickbay.
When Sim grows to a boy of about first grade age and learns to read, he begins having Trip's memories and asking questions about it. Archer decides to tell him the truth, and after a talk in his quarters and a play session with a model spaceship, shows him the unconscious Trip. Sim realises that he's a copy and Archer explains that Sim will need to have surgery since Trip "needs something" from him.
As Sim gets older, he begins helping with the repairs, while T'Pol tells Archer that they need to hurry up with the repairs or else the particles will build up and become dangerous before they're finished. Sim comes up with a solution and runs it by Malcolm and later T'Pol: redirect the phase cannons to fire at the launch bay, so they can launch the shuttlepods. Both agree that it's dangerous, but the only viable option, and Sim admits to T'Pol that he's in love with her and wonders if it's because Trip is.
Sim tells Archer that he wants to pilot one of said pods, but Archer wants Malcolm and Travis to do it instead, making Sim mad at the idea that Archer's being protective of Trip. Thus, they execute the plan, and just when it seems like it isn't working, it does.
Unfortunately, Phlox then realises that in spite of what he previously thought, the operation will kill Sim. Complicating things further, Sim has heard of experiments that might just be able to prolong his life and allow him to live out a normal life, so he's not sure about sacrificing himself for Trip. In Trip's quarters, Sim confronts Archer and points out that he has Trip's memories and could, in a way, by saving him by existing, but Archer insists that the mission requires Trip.
Sim apparently agrees to the procedure, but then Malcolm discovers that he tampered with the launch bay controls in an attempt to escape, only to change his mind when he remembered Elizabeth and decided he didn't want another tragic death to occur, so he decided to agree to the surgery after all. T'Pol kisses him, then says goodbye to Phlox and has the operation. We end on the funeral, which turns out to be Sim's.
Tropes in this episode include:
- Anguished Declaration of Love (virtually a Dying Declaration of Love from Sim's perspective)
- Big Brother Instinct: Sim's reason for not running away in a shuttle pod was because he didn't want someone else to experience the same pain he felt when Trip lost his sister.
- Bittersweet Ending: The episode ends with Trip's injuries cured and the Enterprise up and running again, but Sim dead.
- The Chains of Commanding: Archer takes it upon himself to tell Sim the truth about his existence, as he authorized Sim's creation.
- Continuity Nod:
- Archer still has the flying model spaceship from when he was a kid.
- Sim can think of a worse fate than being stuck in a shuttlepod for the rest of your life: being stuck in there with Malcolm.
- The Diaper Change: At one point during the montage of Phlox looking after baby Sim, he changes his diaper.
- Early Personality Signs: Implied. As a child, Sim apparently behaves how Trip did when he was a child, so the young Sim's curiosity about the ship's technology implies that Trip, who's now an engineer, has been interested in technology from a young age.
- Face Death with Dignity: After a half-hearted attempt to run away from his impending death (he gives up in the launch bay after realizing he's got nowhere to go), he chooses to go back to Sickbay under his own power to save Trip.
- Fake Kill Scare: In The Teaser; at the end the camera pans to show the real Trip at Sim's funeral.
- Godzilla Threshold: The Enterprise crew is in a tough situation — Earth is in danger of being destroyed by the Xindi, many critical systems on the ship are on the fritz and so the ship can't move, and if the repairs aren't completed pronto and they don't get the ship out of the area of space they're in, the hull will be entirely covered in magnetic particles, resulting in all the ship's systems shutting down. This causes the crew to make decisions they wouldn't normally, whether because of ethics (creating Sim) or danger (firing at the launch bay).
- Hilarious Outtakes: In an otherwise dramatic moment.Sim: So your concern for my safety...is about...failing LeVar...
- Human Resources/Walking Transplant: The reason Sim exists is to provide Phlox with samples to cure Trip. In Phlox's defence, he believed that Sim would be able to survive the procedure and live out a normal lifespan (of fifteen days), but he soon determines that this is impossible.
- I Did What I Had to Do: Archer is, pretty obviously, just sick about having to do all this, but he justifies it by saying that the ship needs Trip.
- Interspecies Adoption: Phlox, a Denobulan, raises Sim as his own when Sim is a child. While Sim usually refers to Phlox by name instead of as his father, the two do refer to each other as "a damn good father/son" towards the end.
- Interspecies Romance: This is the point when it's first hinted that Trip (a human) has feelings for T'Pol (a Vulcan). Sim, who's a clone of a human created from a larva, definitely does.
- Jar Potty: One reason Sim doesn't want to live the rest of his days in a shuttle is because he doesn't want to have to pee in a bottle.
- Morton's Fork: Archer has to face several unpleasant ones as Sim grows, as he and the crew come to see Sim as his own person but still "need" him to die to save Trip. At one point Sim suggests an experimental treatment which Phlox didn't mention to him that has a small chance of allowing him to live beyond his allocated lifespan, but Archer can't allow it as it would take too long to determine if it was a success and by that point Sim's DNA wouldn't be compatible with Trip's, which would mean they'd both be dead.
- Never Trust a Trailer: This one makes it look like Trip actually dies—but not without leaving T'Pol Someone to Remember Him By.
- Out-of-Character Moment: T'Pol nervously fidgets with a piece of the particulate, nearly breaks into tears when Sim confesses his/Trip's feelings for her, and later kisses him.
- Screw the Rules, I'm Doing What's Right!: Using a Lysarian desert larva to create a clone is banned, but Archer and Phlox do it anyway to save Trip.
- Series Continuity Error: Having Trip's memories, Sim mentions key lime pie being his favorite dessert. Trip's favorite dessert, mentioned repeatedly, is pecan pie.
- Short-Lived Organism: Doctor Flox uses Lyssarian desert larvae to make a clone of Trip. The clone goes through a full human lifespan in fifteen days.
- Shout-Out: Sim reads The War of the Worlds to Hoshi and Phlox.
- Space Clouds: Enterprise spends much of the episode trapped in a "polaric field", which is something in between a nebula and a Negative Space Wedgie.
- Space Friction: Zigzagged. Sim's plan to save Enterprise from the polaric field relies on using two shuttlepods to tow her up to speed and then letting her coast on inertia, but it takes several minutes at full thrust for the ship to start moving at all in the first place. May be due to the field itself being full of magnetic particles, which would produce a bit of drag.
- Starts with Their Funeral: Seemingly Trip's, but it turns out to be Sim's. Ends with a Burial in Space.
- Suddenly Shouting: Upon telling Archer that Sim won't survive the procedure, Phlox raises his voice to remind him that the whole point of creating Sim was to save Trip.
- Unexpectedly Dark Episode: While the Xindi arc is already darker than most of Enterprise, this episode takes the cake as it involves a baby growing up quickly, angsting over his short lifespan and being a clone of Trip, and ultimately sacrificing himself for Trip.
- Uterine Replicator: Used to grow Sim.
- Toilet Humour: When Phlox changes baby Sim's diaper, he considers using the waste to fertilise one of his plants.
- You Owe Me: Sim says this to Trip just before the operation.
- You Won't Feel a Thing!: Archer and Phlox assure young Sim that his upcoming "operation" won't hurt at all.Sim: Doctors always say that.
