A huge alien vessel overtakes and swallows Enterprise. The ship's engines and weapons are disabled, and her scanners register neither the alien ship nor its energy-ball-like beings, so Captain Archer takes Lt. Reed and Commander Trip Tucker on an away mission that finds Tucker being invaded by one of the wispy energy balls before being returned to his normal state, albeit with memories of having been on Earth. Dr. Phlox's examination reveals no ill effects for the experience.
Tucker is possessed again, and is tracked down in the mess hall where he's been enjoying the sybaritic pleasure of food. The alien says that they are benign explorers who want to experience the corporeal state they long evolved from. In exchange, the crew would have wonderful experiences. Archer demands the release of his ship, and the return of Tucker—which quickly happens… for the most part. The Enterprise is again floating in space, but the engines are still not working.
One-by-one, crewmembers start being possessed and acting out of character, including Reed who goes to Sub-commander T'Pol's quarters and suggests she takes her clothes off so that he may experience sexual intercourse. Ensign Mayweather discovers a sanctuary in the nacelle catwalk area, so Archer moves the non-infected crew back onto the cramped environs of the engines. While there, T'Pol proposes a plan that she will use her more disciplined mind to try to communicate with the beings instead of being infected by them. Archer objects to this dangerous plan, but there are no other alternatives.
T'Pol discovers that the aliens plan to co-opt corporeal bodies to save themselves from their failing ship. The Enterprise Team[clarification needed] hatches a plan to eject the beings by asphyxiating the infected crew. Though he has some trouble with an infected Tucker, Phlox floods the ship with CO
2, and the aliens return to their ship. When the alien ship attempts to recapture the Enterprise, Archer destroys it with two torpedoes.