The Crossing ( episode ) " Enterprise " is captured by a ship of non - corporeal beings who wish to trade consciousnesses with the crew ' s bodies . But these " wisps " may not plan on giving the bodies back . . . Summary . Teaser . is being chased by an unknown vessel approaching at warp 6 . Apart from observing its size to be over five hundred meters wide , the " Enterprise " crew is unable to tell anything more about it – the hull has an unidentified composition and there is no warp signature . Attempts at contact fail , as the ship probably doesn ' t have any transceiver . As the alien ship gains on " Enterprise " , it opens a foward bay hatch and traps " Enterprise " inside . Act One . Captain Jonathan Archer immediately orders tactical alert , only to discover that all weapon systems and engines have gone offline . Looking outside , the crew sees a spacious hall with blue wisp - lights dancing below the ceiling . Learning there are no detectable lifeform s on the ship , Archer takes Lieutenant Malcolm Reed and Commander to investigate the alien ship ' s interior . As the away team , clad in EV suit s , leaves the they detect change in the atmosphere – from one composed mostly of helium , it turns into Human - breathable nitrogen and oxygen mixture . Even though their scanners still don ' t detect any lifeforms , watching the wisp s they grow certain they ' re dealing with sentient beings . Soon one of the wisps approaches them and , through his helmet , enters Trip Tucker ' s head . It emerges a second later , its color changed from blue to golden . Tucker remains conscious , however he is unresponsive and seems disoriented . A little later , the golden wisp returns , switches back with the blue one , and Tucker regains control over his body . Bewildered and not sure about what happened , he recalls watching the away team from above and also a very realistic vision of him swimming at Tarpon Springs with his former girlfriend Lisa . Archer and Reed immediately take Tucker back to " Enterprise " , where Dr . Phlox examines him , but finds nothing out of the ordinary . Although Archer is still worried about the incident , he tells Tucker to work on activating the engines . He also asks Reed to bring the weapons online as soon as possible . Act Two . Back in his quarters , Archer discusses their current situation with T ' Pol . She tells him to consider that the creatures might not be hostile , but Archer remains skeptical . She also informs him of Hoshi Sato ' s unsuccessful attempts at communication and the uneasiness of the crew . In engineering , Tucker is working at the main console when the wisp returns and enters his body again . He exits engineering , leaving behind engineer Michael Rostov puzzled by his strange behavior . Rostov immediately informs Archer about the incident and they find Tucker shortly thereafter in the mess hall , enjoying various types of food . Confronted by Captain Archer , the creature admits switching places with Tucker , but assures he will be back . It also explains that they ' re explorers , just like the " Enterprise " crew , that used to be corporeal beings generations ago and are trying to learn more about their ancestors ' way of living . At Archer ' s request , it releases " Enterprise " from the alien ship ' s bay and soon after the golden wisp returns , returning Tucker back to normal . Again he tells them about reliving some wonderful memories during his time in non - corporeal form and says that " they " offered everyone in the crew to try the experience . Archer however is apparently more worried and orders Reed to take Tucker to sickbay . In his quarters , Archer ponders his distrust of this strange lifeform when he ' s interrupted by the entrance of visibly agitated Dr . Phlox . Just a moment ago , one of the wisps tried to enter Phlox , but without success , probably due to Denobulan physiology being incompatible with the beings . In the armory , another wisp infests Reed , who at first tries to shoot it with a phaser , but to no avail . The creature in Reed ' s body makes several lewd remarks to a female crewman in the turbolift , and when the confused woman leaves the lift , he makes his way to T ' Pol ' s quarters . After voicing Reed ' s opinion about T ' Pol being the most beautiful woman on board , he makes some rather crude advances towards her . She at first thinks him drunk , but soon realizes what happened and summons Archer and a security team . As this creature isn ' t as cooperative when asked to leave Reed ' s body , Archer orders him locked in Reed ' s quarters . Hearing the grim news , Tucker and his engineers hurry to get the engines working . Tucker finds that Rostov had also been infested and soon the bridge is flooded by reports of similar incidents throughout the " Enterprise " . Archer orders the security teams to have anyone acting strange confined to their quarters , then asks T ' Pol and Phlox to find a method of detecting infested people . Act Three . The engineering team manages to get the impulse engine s back online , but Archer decides not to move until they find a way to bring back Reed and the others . Meanwhile , Phlox and T ' Pol discover raised levels of acetylcholine in the autonomic nervous system of the possessed people and program scanners accordingly , thus gaining ability to identify infested crewmembers . On his way to a warp nacelle , Travis Mayweather spots a wisp approaching him and starts running away . During his frantic escape , he accidentally finds out that the wisps are unable to penetrate the osmium alloy shielding of the catwalk . Hearing about existence of such safe area , Archer immediately orders transferring command functions and evacuating all non - infected crew to the catwalk . Despite this ray of hope , there is another grim discovery : Hoshi Sato has been infested and tries to once again convince Archer for the crossing . It turns out that 58 non - affected crewmembers retreat to the catwalk , leaving outside Dr . Phlox ( who is immune to possession ) and 24 infested crewmembers locked in their quarters . With situation more or less under control , T ' Pol asks the captain to allow her to leave the catwalk . She wants to discover more about the creatures and their intentions by coming into contact with one of them . She believes that with Vulcan mind discipline she should be able to resist the possession . Meanwhile , Sato ' s resident summons Dr . Phlox to her quarters , saying she has a broken leg and requires medical attention . When he examines Sato and finds she is in fact unharmed , the alien possessing her violently attacks Phlox , screaming she needs to get the rest of the crew . He manages to subdue her using a hypospray and goes to assist T ' Pol . T ' Pol carries out her plan and discovers the true motives of the aliens . It turns out they can ' t survive in space without the ship , which is breaking down – and they ' re unable to repair it . They need to find corporeal hosts in order to survive , and 82 of them are trying to get " Enterprise " crew as their hosts . T ' Pol also reveals there are hundreds of these creatures on their ship , hunting for more vessels with compatible hosts . Act Four . Captain Archer is adamant about saving the infested crewmembers , so he , T ' Pol , and Phlox decide to try flooding the ship with carbon dioxide . As T ' Pol learned that dead bodies can ' t serve as the aliens ' hosts , suffocating the possessed will force wisps to leave . Purging CO at the right moment will give Phlox enough time to resuscitate the victims . Phlox puts on an EV suit and starts working on the ventilation system , with Archer and T ' Pol giving him instructions via communicator . However , it turns out that one of the wisps has found its way into the sealed catwalk , and once again possessed Tucker . When he hears about the plan , he storms out , beating Mayweather who tries to catch him . Tucker finds Phlox and tries to stop him , but after short struggle , Phlox opens the CO valve and Tucker falls unconscious . When the gas gradually fills all decks and the infested people suffocate , the wisps escape their dying hosts and return to their own ship . When the last wisp leaves , " Enterprise " goes to full impulse speed , but the wisps aren ' t willing to give up . They move to recapture " Enterprise " , with their ship ' s maw wide open . However , it seems that Reed and his team managed to get at least some weapons working and two spatial torpedo s fired into the ship ' s open hatch tear it apart from the inside . On the " Enterprise " , Phlox revives Tucker ( who remembers only he had " just been at a barbecue " ) and takes him along , stating that they " have a lot of doors to unlock " . Memorable quotes . " " It ' s like we ' re in a belly of the beast . " " " " We have no reason to believe their motives are hostile . " " " " They ' re holding my ship hostage . " " " " We don ' t know that . " " " " We don ' t ? Look out there ! You see any stars ? Our engines are offline , our weapons . . . seems kind of hostile to me ! " " " " I suppose it depends on how you look at it . " " " " Something smells funny . " " " " Are you a female ? " " " " Sir ? " " " " Your gender . . . you are a female , correct ? " " " " Last time I checked . " " " " I am a male ! " " " " I ' m aware of that , Lieutenant . " " " " There seem to be a number of anatomical differences . . . " " " " Sir ! " " " " Are you aware that you are the most attractive woman on board this ship ? " " " " If we are to engage in mating , it would be easier if you disrobed . " " " " Enough ! Humans don ' t like doing things without their consent ! " " " " I understand how you may be frightened by all this . Losing your substance , existing as perceptive energy . But you ' ll be grateful once you ' ve made the crossing , I promise you . " " " " We ' re kind of fond of our substance ! " " " " I ' ve reached the access tube , captain . " " " " Good . Now pull off the panel . " " " " It ' s not coming off . " " " " It ' ll come off . You just need to use a little muscle . " " " " I ' ve used every muscle I ' ve got – it won ' t budge . " " " " Try using your foot for leverage . " " " " Good suggestion . " " Links and references . References . acetylcholine ; anatomy ; atmospheric recycling manifold ; autonomic nervous system ; barbecue ; bread ; camera ; carbon dioxide ; carbon dioxide tank ; central ventilation ; ; catwalk ; Celsius ; Cole ; corporeal ; crossing ; deuterium injector ; deuterium pump ; dilithium matrix ; Earth ; EV suit ; explorer ; fine motor skills ; Florida ; gender ; God ; hand scanner ; helium ; hull plating ; impulse engine ; ; logic ; mating ; neural pathway ; New Zealand ; nitrogen ; noncorporeal being ; November ; osmium ; osmotic filter ; oxygen ; phase cannon ; power grid ; physiology ; sexual reproduction ; ; snow - sailing ; spare ribs ; spatial torpedo ; subspace ; support plate ; swimming ; tactical alert ; Tarpon Springs ; temperature ; transceiver ; transfer line ; ; turbolift ; Vulcan ; Vulcan database ; warp engine ; warp coil ; warp nacelle ; warp signature ; wisp ; wisp ' s ship ; xenon