Sisko is hosting a party in his quarters and showcasing his skill at handmaking New Orleans cuisine, which amazes his comrades. Dax discovers Jake's discarded keyboard and laments that none of her hosts had any musical ability. However, she promptly starts playing an interesting tune with surprising skill. Trying to remember how the rest of the tune goes, she harshly silences Bashir to let her concentrate, but she still has no idea where it came from.
While playing chess with Sisko the next day, Dax is still fixated on the tune. Her distraction allows Sisko to put her in check. Suddenly angry, she accuses him of cheating and rage-quits. Kira tries to speak with her about the incident, but Dax doubles-down on her uncharacteristic behavior and chews Kira out for taking Sisko's side. As she walks away through a seemingly abandoned promenade, the lights suddenly go dim, and she spots a mysterious figure in a white mask. It removes its mask to reveal another mask, and Dax tears that one away to reveal a third mask. But then she bumps into Quark and snaps back to reality, realizing that the whole episode was a hallucination.
Dax seeks Bashir's help. He researches her symbiont's history and notes that Torias, the host before Kurzon, went into a six-month-long coma before his body was sacrificed and the symbiont was transferred to Kurzon. Bashir discovers that Dax's body is in the process of rejecting her symbiont. If that happens, she will be sacrificed to save the symbiont. Dax, Bashir and Sisko journey on the Defiant to Trill to consult the experts. Along the way, Dax visits Bashir's quarters for a little heart-to-heart, and she falls asleep on the bunk below him. On Trill, Dax is subjected to a battery of tests under the direction of Dr. Renhol. Afterwards, Dax has another hallucination of encountering the masked figure and then being attacked by two Trill orderlies wearing uniforms from last century.
Out of options, Dax and company visit the Guardians, who care for unjoined symbionts in the Caves of Mak'ala. A Guardian named Timor asks about Dax's "dreams," and she states that they're more like memories. He hypothesizes that the problem stems from one of her previous hosts. Back on the ship, Sisko has discovered that the piece of music in Dax's head was written by Joran Belar. His picture causes Dax to hallucinate the masked man killing a Trill doctor. In reality, Dax collapses.
With Dax's condition worsening and rejection imminent, Sisko and Bashir return to Timor, but he's suddenly become very unhelpful and fearful. Researching more about Joran, they discover that his file was mysteriously wiped, but he happened to die on the same day as Torias Dax. They get in touch with Joran's brother, who recalls that Joran was a symbiont initiate with a violent temper who killed the doctor who rejected him and was then killed while fleeing — or at least that was the official story put out by the Symbiosis Commission. They hypothesize that Joran somehow acquired the Dax symbiont from Torias before he died.
Dr. Renhol makes the call to sacrifice Jadzia and place her Dax symbiont in a new host, but Sisko and Bashir stop her by confronting her on the discovery they've made that could tear Trill society apart. Joran was indeed joined to the Dax symbiont for six months before his death, despite his psychological instability. This means that the Symbiosis Commission's claim that only a small percentage of Trill's population are suitable hosts is a lie. The Commission purged its records and placed a memory block on the Dax symbiont to hide Joran's existence, but the block is degrading and the secret is in danger of being revealed. Renhol admits that almost half of the population could be viable hosts, but such knowledge going public could sow chaos throughout Trill.
Sisko forces Renhol to let Dax decide whether to allow the memory block to fade completely and attempt to acclimate to Joran's chaotic presence in her mind. Dax goes to the Caves of Mak'ala and wades into one of the symbiont pools. An image of Joran emerges from the pool, and Dax welcomes him to become a part of her. They embrace, and Joran's image merges with her. Back on the station, Sisko checks in on Dax, who notes Bashir has already done the same. After assuring the commander that she is OK, Dax sits down and begins playing Joran's song.
Tropes:
- Bizarre Alien Biology: Odo states that he has no need for food, making you wonder about his source of energy.
- Blackmail: Sisko gets Dr. Renhol to heal Jadzia by threatening to expose the Trill's secret.
- Canon Discontinuity: Getting hijacked by Verad apparently doesn't merit as a "Traumatic event" for the Dax Symbiont.
- Cloud Cuckoolander: Guardians spend all their time underground caring for symbionts and therefore become somewhat eccentric.
- Dark Secret: The Trill Symbiosis Commission is hiding the fact that almost half of Trill are compatible with symbionts.
- Desk Sweep of Rage: Jadzia takes out everyone on the chess boardnote when she suddenly gets angry at Sisko.
- Didn't See That Coming: Nobody expected someone as mentally unstable as Joran to be able to bond with a Symbiont.
- Ear Worm: The melody that Jadzia plays during The Teaser. And like any good earworm, she makes sure it sticks in Sisko's mind as well.
- Faking Another Person's Illness: The Symbiosis Commission altered Torias Dax's medical record to report he was in a coma for six months before the Dax symbiont was transferred to Curzon, in order to cover up the six months that Joran Dax existed.
- Government Conspiracy: The Trill Government and the Symbiosis Commission have been lying for centuries about the relationship between the symbionts and the Trill species. The truth is that nearly half of all Trill are capable of being a host, but with so few symbionts the government invented the "only 1 in 1,000" lie to prevent symbionts from turning into commodities to be bought by the highest bidder or fought over as prizes.
- Heinousness Retcon: Joran, the secret former host of the Dax symbiont, whilst always a murderer and presented as psychologically unstable. As presented here, he was a regular killer with only one victim, someone he had a motive to kill. In all his later appearances he has more victims and is full-blown deranged, with even Quark somehow knowing it. To the point that Ezri summons him to help her get an insight into the mind of a psycho when there is a Serial Killer loose on the station.
- Laser-Guided Amnesia: The Symbiosis Commission implanted a "memory block" in Dax to prevent memories of Joran from surfacing. The issue is that the block is deteriorating, causing bits of his memories and personality to leak out.
- Leitmotif: The melody Jadzia plays in the cold open becomes Joran's theme for his subsequent appearances in the series.
- Malevolent Masked Man: Jadzia has recurring hallucinations of one. It's her memories of being Joran trying to resurface.
- Mandatory Line: Quark's only contribution to the episode is getting bumped into.
- O.O.C. Is Serious Business: The first sign of trouble is when Dax tells everyone to shut up so she can concentrate on the mystery song. Her temper only gets worse before she realizes something is wrong.
- Past Experience Nightmare: Jadzia hallucinates being attacked and restrained by members of the Trill Symbiosis Commission...wearing uniforms from over a hundred years ago.
- Rage Quit: When Sisko puts Dax in check, she accuses him of cheating and then sweeps all the pieces off the board before storming out.
- Screw the Rules, I'm Doing What's Right!: Sisko doesn't care much about Trill politics, but he will save Jadzia's life, even if he has to effectively blackmail the Symbiosis Commission to do it.
- Sherlock Scan: Timor can tell that something's wrong with Jadzia at a glance and figures out the rest by simply laying a hand on the implanted Dax Symbiont.
- Supreme Chef: The episode opens to the Siskos preparing a meal for the senior staff, with Ben stating that he learned all about cooking from his father, a successful restaurateur.
- Telepathy: Trill guardians seem to have this. It may be a requirement for the job, or it could be something they develop with long exposure to unjoined Symbionts (who communicate via bioelectricity).
- Took a Level in Jerkass: Jadzia early in the episode. It's the first sign that something is seriously wrong.
- Unperson: The Trill government tries to purge all mention of Joran from their records and Dax's memory, causing the problem in the first place.
- Well-Intentioned Extremist: The Symbiosis Commission have to deceive the public about the percentage of join-worthy Trill to keep the Symbiont species from becoming nothing but a commodity.
- Why Did It Have to Be Snakes?:
- Dax confesses to Bashir that she'd always been afraid of doctors. Julian tells her that he used to feel the same way.
- Curzon Dax fell out of a tree once, and as a result, Jadzia is uncomfortable with heights.
