“Cathexis” is episode thirteen of season one of Star Trek: Voyager.
Captain Janeway is recording her personal log, how it is good to get away from being a captain and how she has just started a new holonovel set in Ancient England. It appears to be a period drama of some type where the captain is the governess for a widower, one who tells her to never, ever visit the fourth floor. Not at all creepy. Harry contacts her from the bridge, though; Chakotay and Tuvok’s shuttlecraft has been picked up on long range sensors. The shuttlecraft isn’t responding to hails and bears signs of damage. There are two faint lifesigns on board. Janeway tells Harry to have Tuvok and Chakotay beamed directly to sickbay.
In sickbay, the Doctor says that both took a blast to the head. Tuvok has simple concussion; Chakotay has had all the bioneural energy drained from his brain. The Doctor can keep his heart beating but, other than that, there isn’t a lot he can do. Chakotay is brain dead.
Tuvok says that the attack only lasted a few seconds, but it was highly effective and they are lucky to be alive. They had completed their trade mission and were heading towards the rendezvous when they passed a dark matter nebula. A ship emerged from the nebula and attacked; it wouldn’t respond to hails. An energy discharge penetrated the cabin but Tuvok was able to set the autopilot before being overcome. He saw the alien ship flying back into the nebula. There was no time for analysis, but the shuttle’s sensors may have recorded something useful. The captain wonders why someone would extract the bioneural energy; the Doctor is more concerned about how. So, she orders a course set for the nebula.
Tuvok says that the sensor data has been erased from the shuttle; Janeway tells him to send it to B’Elanna for further analysis, once she’s finished in sickbay. They are unable to scan inside the nebula, so Janeway starts modifying the sensors when suddenly they lose all sensor contact with the nebula. Harry says they have altered course and Tom confirms this; they have completely come about, but it wasn’t him. Harry checks the navigational computer and it appears to have been done by the helm. Tom reiterates that it wasn’t him, and that helm control is working perfectly. The captain tells him to transfer control to Harry whilst he checks his controls.
B’Elanna is in sickbay performing a ritual over Chakotay; the Doctor says she could have asked before adorning the place with animal remains. B’Elanna explains that it’s a medicine wheel, a talisman used by Chakotay’s tribe. He once showed her how it worked and told her to perform a special healing ritual if anything ever happened to him. The Doctor points out an error she has made; it is his business to know treatments, including psychospiritual beliefs. He doesn’t think it would be much help currently, though.
Kes is in her quarters reading, when she suddenly senses something, or someone. Something does seem to be watching her. She explains it to Neelix in the galley; he asks if it’s similar to last week. No, this time she felt as if someone was in the room with her.
Voyager has changed course again and Harry tells the captain he is locked out of the helm. He’s been blocked from navigational control. Tom couldn’t find any problems but B’Elanna says that she saw him in navigational control a few minutes ago. Tom says that isn’t true. Janeway is concerned that Tom is having problems with his memory, and tells him to go to sickbay to be checked out. Tuvok enters as Tom is comparing the Doctor to an old family doctor and hasn’t found anything wrong. Tuvok has found Tom’s DNA on the console used. The Doctor is going to run another scan.
The ship is heading back to the nebula when suddenly power goes offline and the warp core starts shutting down. It seems that B’Elanna crashed the computer, locked down the bridge and stopped the ship cold. Only she doesn’t know what anyone is talking about. In sickbay, the Doctor has found that a different energy pattern appeared when Tom shut down navigation control and when the course was altered. The same for when B’Elanna shut everything down. An unknown alien entity seems to have taken control of them.
It seems that there is an entity that could be in any one of them. Except, according to Tom, for the Doctor. If it could control computers directly, it would have done so. So, the Doctor is the only person they can trust. Janeway decides to transfer all her command codes to the Doctor for now. No, he isn’t in command; he’s a failsafe.
With a body-hopping entity around, a bit of paranoia grips the crew. Especially Neelix, after Kes gets hurt; he goes off on some wild flights of paranoia until the Doctor calms him down. Whatever the entity is, it seems to really not want Voyager to return to the nebula.