Doctor Bashir treats Odo in the Deep Space 9 sickbay, still unable to make any significant progress in curing his sickness. He estimates Odo has one week, perhaps two, before dying. Odo persuades Kira to leave his bedside to accompany Damar on a mission with the Cardassian Resistance, for his sake as well as hers. Elim Garak reminds Kira that they need to leave quickly before the Dominion border patrols are changed. Odo appears to be in an advanced state of decomposition, yet this does nothing to dampen their love for one another. Starfleet now has the Breen energy-dampening weapon Kira and the others were able to procure, and a defense is being worked on. Kira reluctantly leaves Odo's side. When Captain Sisko inquires of Odo's prognosis, Chief Miles O'Brien suggests that a medical cure is not the only option they have been pursuing, at which point Sisko demands to know the whole story. Doctor Bashir reluctantly discloses his belief that Odo's sickness is a virus created by Section 31 to wipe out all Changelings, leaving Sisko shocked that people who call themselves Federation citizens are attempting to commit genocide. Bashir also says that he has transmitted a report to Starfleet Medical, falsely claiming to have found a cure for Odo's sickness, in order to lure a Section 31 operative to the station; once captured, the agent would be scanned with Romulan mind probes, to help point Bashir in the right direction of finding a cure. Sisko then asks why they didn't tell him. Bashir answer that if they told him, then he'd alert Starfleet Command and Section 31 would cover up their tracks once they realize they were discovered. Despite that what they're doing is illegal and unethical, Sisko approves. Later that evening, O'Brien stumbles across Bashir throwing darts in Quark's; each man is restless and feeling down in the dumps. Bashir tells O'Brien that, after thinking over the conspiracy to infect the Founders with the disease, has concluded that at least seventy-three people must have been involved in the plot; a fact that leaves a very bitter taste in his mouth. The two friends each view Section 31 as an evil that's crawled its way into the heart of the Federation, and that it must be destroyed. Afterward, Bashir awakens in his quarters to find Section 31 operative Luther Sloan sitting comfortably in a chair overlooking Bashir's bed, as he normally appears, saying he has another assignment; but this time, Bashir is ready for him. The doctor activates a containment field, trapping Sloan where he sits. Sloan is impressed, but indicates that turning him over to security won't do any good. Bashir tells Sloan that he needs the cure to the morphogenic virus; Sloan is confused, he thought Bashir had already had it but he soon realizes he doesn't. Bashir tells him he just been "had", then stuns Sloan unconscious with a phaser. Sloan awakens in sickbay, immobilized with a force field encompassing his body. Sloan asks O'Brien if he has a family, implying that if he dies, Section 31 will harm them. Yet Bashir doesn't believe him and tells Miles to not to listen to him. Bashir deduces that Sloan must have known the cure in order to find it in Julian's lab and destroy it. As Bashir and O'Brien prepare to use the Romulan mind probes on Sloan, Sloan activates a neuro-depolarizing device in his brain, killing himself. Bashir stabilizes Sloan's body, but the higher cortical functions in his brain will cease within the hour, so Bashir prepares a multitronic engrammatic interpreter to link minds with the dying Sloan; Miles insists on accompanying the Doctor on his travel through someone else's mind. Bashir explains to O'Brien that when they are ready to exit, he will use his genetically-enhanced nervous system to raise his blood pressure, thus sending a signal to the device to pull them out. When they activate the mind link, they find themselves in a turbolift, which is merely an abstraction in Sloan's mind. The turbolift doors opens to a recreation of DS9; a cooperative Sloan tries to tell the two the cure, which is a simple nucleotide sequence but the dominant Sloan personality is preventing him from telling the last part, so he leads the two mind-travelers to a reception, being held in Sloan's honor, where he delivers a farewell speech to his family and friends, apologizing for all the pain he has caused in his life. After he finishes, he prepares to give Bashir and O'Brien the cure on a PADD, but suddenly another Sloan appears, killing the first (cooperative) Sloan with a phaser, and running away down a corridor of Sloan's dying, yet still active, mind as cooperative Sloan's party disappears. Bashir and O'Brien receive phaser wounds from a character "guarding" Sloan's mind. The wounds are causing them physical pain, meaning that Sloan is sending sensory stimuli to their brains, as well as thought patterns. When Bashir is unable to disengage the mental connection, the two men fear they will die (in reality) because their minds are linked to a dying mind; they ponder friendship, marriage, love. As O'Brien wishes he had written Keiko a goodbye letter, Bashir confides that he loves Ezri, but has never told her. They then see... the light at the end of the corridor. They resist the urge to quit; instead, they regain their bearing, and head off down the corridor. Suddenly, Bashir and O'Brien wake up with Sisko, Worf, and Ezri around them. Bashir tries furiously to save Sloan and the knowledge of the cure, but it is no good and he dies. Devastated, Bashir tells Odo that he has no hope of finding a cure. Later, Bashir tries to take his mind off the matter by reading A Tale of Two Cities, but finds that after turning the page, the book simply begins again from the start. Knowing the book can't be misprinted, Bashir realizes that he and O'Brien are still in Sloan's mind, and that is another trick being played by Sloan, who is trying to lure Bashir and O'Brien to their deaths. When they finally reach the "inner sanctum" of Sloan's decaying mind, he tempts them with information tablets about every aspect of Section 31. However, O'Brien realizes that it is one final ploy by Sloan, meant to distract them from finding what they are seeking: a cure for Odo. Miles finds the correct tablet, and persuades Bashir to reluctantly walk away from the information tablets which could lead to the downfall of Section 31. Bashir wakes up in sickbay with Sisko, Ezri, and an attending medical staff. O'Brien awakens, and promises that will be the last mind link he is ever a part of. Sloan is dead, but Bashir has discovered the cure. Later, having synthesized the cure, Bashir injects it into Odo, who experiences a quick and complete recovery. Later that night, Bashir is playing darts again in Quark's, and O'Brien comes by to invite the doctor to dinner. O'Brien find a bottle of the 'good stuff' which is older than Bashir, and the two friends share a toast to 'aging gracefully and to Odo'. Bashir accepts the dinner invitation, and reminds him that Sloan had the perfect bait for Bashir with all the information on Section 31, however O'Brien was the one that saved him. The two drink a toast to friendship and leave for the dinner which Keiko has prepared.