A big WTF ship approaches at warp 6, doesn't respond to hails and, er, eats Enterprise. Yo, evasive manouvres, anyone?
Archer takes a shuttlepod out and he, Trip and Reed wander around for a while. There's some ghosty things floating around, but that's it. One of them jumping into Trip, causing him to float around a bit or something. They return to Enterprise, where Phlox gives him a clean bill of health.
Back in engineering, one of the ghosty things takes over Trip again and sods off. They find him in the mess hall having a meal. They have a surreal conversation with ghosty and ask him they can have the real Trip back, please. The ghosty aliens let Enterprise out and return Trip to his body. Woo, random New Zealand namecheck! Trip suggests the others have a go out the whole out-of-body thing, and Archer sends him to sick bay.
Later on, one of the aliens takes over Reed's body and starts acting creepy towards women. And then goes and asks T'Pol to take her clothes off. "Have you been drinking?" Sure, there are bizarre body-stealing aliens around, and the first conclusion she draws is that Reed's drunk. Evidently she's never seen Reed drunk, as he's more like Dudley Moore than some sort of creepy stalker. Archer arrives and locks creepy alien Reed in his quarters.
More people get bodyswapped with the aliens. Trip gets the engines back online, but Archer says they can't leave til they get their crewmen back in their bodies. Phlox has found a way to tell pod-people from normal people. Mayweather establishes that the catwalk in the nacelle is shielded from the aliens, and Archer orders everyone up there so they can reuse the set. Hoshi's been podded! Oh noes!
T'Pol thinks she can metnally communicate with the aliens or something. Meanwhile, podHoshi fakes a broken leg shot she can attack Phlox, who responds by tranqing her. Hehehehehehehe. A ghosty jumps into T'Pol and she stops moving. While Phlox is trying to work out what to do, she kicks the ghosty out - the alien ship is deteriorating and they're trying to take over the crew to escape it.
T'Pol suggests they leave, but Archer doesn't want to abandon a third of the crew. Trip's gone missing. Tsk. Archer talks Phlox through fiddling with the ship's life support system... Oh, Trips been podded again. He leaves the nacelle and interrupts Phlox's work. There's a fight, but Phlox manages to complete his work, and all over the ship, the podded aliens fall over and leave their host bodies.
Enterprise starts leaving, followed by the alien ship. Archer lobs in a couple of torpedoes and it blows up. Teh end.
That was... odd.