“The Host” is episode twenty-three of season four of Star Trek: The Next Generation.
Dr Crusher narrates some items in her personal log, before finishing by saying there is someone new in her life. She is making out with that someone new in a turbolift when it stops and Data gets on. Data wants to go into a matter and the doctor’s attempts to avoid this fail. The other, Ambassador Odan, isn’t feeling well and will return to his quarters. The doctor asks if he’s having headaches and will bring a hypospray whilst Data inputs the information. In his quarters, Odan checks his stomach, which starts to bulge and move, and uses a device on it.
Later, the doctor is with Odan in the latter’s quarters; Odan admits he was worried Data would barge in. Dr Crusher says they should go back and check on Data, or he may come and check on them. She also wonders if this is interfering with the ambassador’s work. No; he’s done as much as he can, and he can’t keep on his mind anyway. The doctor is attempting to leave when Captain Picard contacts Odan; the representative has arrived and they will meet in the observation lounge.
Governor Leka Trion is telling the captain that the situation is getting worse. Troi asks the doctor where she was; a patient had a minor emergency. Odan enters and Picard introduces him to the governor. The governor knew Odan’s father; he kept their people at peace. Data checks to see if the doctor helped with Odan’s headache.
The inhabitants of the two moons of the governor’s planet are squabbling, though the mainworld tries not to get involved. Alpha moon generates energy by tapping the planet’s magnetic field. Beta is suffering environmental problems as a result and is already suffering medical repercussions. Alpha won’t give up its energy source and Beta is accusing them of genocide. Both moons are prepping for war and if that happens the people on the planet will take sides. Captain Picard is saying the ambassador should beam down, but Odan wants to take a shuttle, even though the governor advises against this. Afterwards, with only Troi and the captain left, Troi says she feels fluctuations of emotion from Odan, but they know so little about the Trill.
Troi heads to the ship’s spa and finds Dr Crusher there. After winding the doctor up a bit, Troi tells her she’s in love. And she didn’t need her empathic sense to know that. The doctor starts examining her feelings, but she hasn’t felt like this in a long time. And she likes it.
Odan meets with the captain in his ready room. Odan has no plan; he needs to meet the people involved first. The captain’s staff has been very helpful briefing him on the problems. Especially Dr Beverly. Going into a little too much detail about her. Odan wonders if she’d ever leave Starfleet. It’s not for the captain to say.
Commander Riker is going to pilot Odan’s shuttle down. However, when they leave the Enterprise, an unknown vessel appears and opens fire on them. Odan is injured and the shuttle is breaking up, but he tells Riker that the transporter would kill him.
In sickbay, the doctor thinks Odan has a parasite. Except Odan states he is the parasite. The body is just the host. The Trill are a joined species, host and symbiote. His host body may be dying, but the Trill will send a replacement.
Dr Crusher briefs the staff. The host has died but the symbiote is alive. Odan was the one who negotiated the last treaty; it wasn’t his father, just another host. Transporters can damage the symbiote. A new host is on its way, but its 40 hours out and the doctor can only keep Odan alive for an hour or two. Data offers himself as a temporary host, but it requires a biological entity. And the dispute is getting worse. So, Riker offers himself.
Dr Crusher has problems dealing with the fact that Odan is now in a different body. So does everyone else. And the symbiote takes a physical toll on the commander.
The Trill are rather different in this portrayal of them to how they will be in Deep Space Nine, which is only a couple of years away. Their appearance is different, host and symbiote are different and, in DS9, it’s clear that it’s been known for some time that the Trill are symbiotes. Nor do they have problems with transporters.