“The Crossing” is episode eighteen of season two of Star Trek: Enterprise.
A large ship is approaching Enterprise at warp 6. Their sensors are having problems reading it, T’Pol says it isn’t in the Vulcan database and not only is it not responding to hails, Hoshi can’t even detect a transceiver array. Doors open on the other ship and Enterprise is engulfed.
Weapons are offline and warp and impulse engines are down. Sensors can’t penetrate their engulfer’s hull, but life support is operational. T’Pol can’t detect any biosigns. Looking to the rear of Enterprise, they spot glowing wisps of something. T’Pol can’t detect any elements that their sensors can identify. Atmosphere in the huge bay is helium with traces of xenon.
The captain heads out in a shuttlepod with Trip and Reed. They’re wearing environment suits but, once they step out, the atmosphere changes to breathable and the temperature rises to comfortable. They can’t get a read on the glowing wisps. One of the wisps enters Trip, and one of a different colour leaves. They swap again and Trip asked what happened. He seemed to be up with the wisps, looking down on them but not with eyes, then was with Lisa back home in Florida.
Back on Enterprise, Phlox reports no parasites, lifeforms or wisps of smoke in Trip. The captain says Trip had an out of body experience; the doctor says these are a common hallucination. But he’s fine.
T’Pol enters the captain’s ready room. She says they have no reason to believe the wisps are hostile. The captain points out they are holding his ship hostage and they have neither weapons or engines. That seems hostile. Hoshi is trying to communicate, unsuccessfully. The crew is concerned but remaining calm.
Trip is in engineering when one of the wisps enters him and another one leaves. One of the crew contacts the captain and reports that Trip is acting strange and has left engineering. Trip isn’t answering comms and is found in the mess hall by Captain Archer, T’Pol and Reed with a lot of food. He says he’s never eaten before. Trip is exploring another realm, the realm of the one now in him. He’s no longer corporeal.
Whatever is in Trip says they live in subspace and travel through it. They’re explorers, too. It’s a long time since they encountered corporeal beings and once the first crossing was done, they discovered they were compatible. Once, they used to be corporeal too. Now they can learn how their ancestors lived. The captain wants Trip back and the ship released. Enterprise is disgorged and the alien says they should open their minds to new possibilities before Trip returns. Trip explains what he saw. Anyone on the crew can try. The captain still wants him checking out.
It’s going to be some time before engines are back online and Dr Phlox visits the captain in his ready room. One of the beings tried to enter him, but it seems their physiology was not compatible and it left almost immediately. It was disturbing; the lifeform was trying very hard to reach him.
Reed is in the armoury when another appears. Despite shooting at it with a phase pistol and fleeing, it takes control. Which leads to an awkward conversation with a female crewmember and the worst pickup line ever with T’Pol. The others realise that Reed has been taken over by one of the wisps without his permission, and he’s only the first. More crew are taken and Enterprise can neither leave nor get their missing crew back. They only have their bodies, occupied by other beings.