In media res Archer addresses a crowded armory about the difficult loss of a shipmate - Dead Trip (RIP Kellie Waymire, creepy teaser timing). Two weeks earlier Live Trip neuropressures the tender Vulcan ankles of his moaning callipygian partner, then the demographics stop and the story starts. Trip performs a warp test right as NX-01 enters a polaric field, a flood of ferric diamagnetic nucleonic particles - iron barnacles - sticking to the hull like flung poo threatening to extinguish all ship systems.

More bad news: Trip's in a coma, but Phlox has an illegal and not-proposed-lightly plan: use a Lyserian Desert Larvae (a slimy papier-mache potato-mummy capable of replicating alien DNA) to grow a Disposable Trip for replacement parts. Earth needs Enterprise, Enterprise needs Trip, so Archer orders the clone created. Dubbed "Sim" and growing at an accelerated rate, he retains Coma Trip's memories. Kid Sim takes to Porthos, a tortured accent, and breaking Archer's models. His personal questions disturb Archer who dehumanizes him by introducing the vegetable behind the curtain. Assured of a painless procedure he takes the news of his impending vivisection well. Teen Sim makes a failed T'Pass but Adult Sim melts her Vulcan heart by declaring his affection openly.

Phase cannons blast the bay doors barnacle-free so (secret-word!) Mayweather and Reed might display exceptional bravery towing NX-01 to safety using fusion overload-ed shpods. Phlox realizes Sim won't survive the transplant but Sim wants more life, Phlucker, using an enzyme to stabilize his lifespan. Refusing delays that risk his comatose engineer Angry Archer confronts Sim in Trip's quarters and threatens to kill him. Sim attempts an escape but with no place to go he's trapped, left to rue his eight-day lifespan and snark about being stuck with Malcolm. He rationalizes his sacrifice with memories of Elizabeth Tucker and asks Archer to warn Reset Trip to "watch his ass."

After spending his last hours with Porthos an emotionally overwhelmed T'Pol delivers a delicious kiss as a going-away present. With dignity he reports to Sickbay and before Phlox kills his damn good son, Sim tells Reset Trip, "You owe me one." Rejoining the teaser Archer assures his crew - and Reset Trip (improved with Sim's memories?) - that all citizens of earth do. Sim guessed this dismal fate was what he "was meant to do" but all I'm sure of is that this episode is damn good, like the similarly controversial episodes "Dear Doctor" and "Cogenitor." Scientifically the doppelganger cum DNA-memory is rubbish but as a plot device it succeeds immensely.