The Bajoran Gratitude Festival, an annual celebration, is about to get underway, and both Kira and O'Brien await the arrival of their loves. But while Kira's encounter with Bareil is sweet, O'Brien's long-anticipated reunion with his wife Keiko is strained — she is exhausted and their daughter, Molly, is sick. To make matters worse, Lwaxana Troi also arrives, and immediately seeks out Odo, hoping for a romantic rendezvous, but he is uninterested. Similarly, Kira is too busy setting up for the festival to spend time with Bareil, and Keiko is too tired to enjoy her time with her husband. But at the opening festivities, Lwaxana experiences a brief headache, which Bareil and Jake seem to feel simultaneously.
As the festival gets underway, Bareil and Kira finally find some time to spend together, but are interrupted by Jake, who insists on speaking with Kira in private. Once Bareil leaves, Jake shocks Kira by saying he is in love with her. Bareil, meanwhile, wanders to Dax, and finds himself suddenly smitten with her. As all this happens, Lwaxana continues her futile pursuit of Odo, then has another brief headache near Dax, who appears to feel it also. O'Brien's romantic endeavors are also thwarted as Keiko says her research on Bajor will keep her there for another few months, then storms away from her angry and hurt husband.
O'Brien talks with Quark, where the proprietor treats him to a taste of the Ferengi philosophy on women, inadvertently showing O'Brien how much Keiko means to him. Meanwhile, Kira finds Bareil, and is hurt when he dismisses her as no more than a friend. Dax, while hiding from Bareil, has joined Sisko, and surprises her friend with the announcement that she is really in love with him.
Bashir's examination of Dax reveals nothing wrong, and she pretends it was all a joke until she and Sisko are alone again, at which point she kisses him. Meanwhile, O'Brien speaks to Keiko through her locked bedroom door, telling her he will resign to stay together, but Keiko says she needs to think about it. Later, Odo, Lwaxana, and Bashir see Kira on their way to Sisko's upcoming party, and Lwaxana feels another headache, at which Bashir and Kira react. The two of them then go to the Infirmary, where they immediately kiss passionately.
At the party, Sisko watches in horror as Dax chases him, Bareil chases Dax, Bareil hits Sisko, Dax slugs Bareil, Jake moons over Kira, and Kira and Bashir can't keep their hands off each other. Keiko arrives at the party in a stunning red dress, walks up to her husband and tells him not to resign, then kisses him. Quark shows up, then proclaims his undying love for Keiko. Luckily, Sisko and Odo notice that before Quark saw Keiko, Lwaxana had a headache, after which Quark seemed to feel the same headache. Bashir discovers that Lwaxana has Zanthi Fever, in which Betazoids experiencing a headache from the condition project their amorous feelings for someone onto those in close proximity. To Sisko's surprise, it only affects people who already have a pre-existing latent attraction. Bashir cures her and says everyone will be back to normal in a few days. But for Keiko and O'Brien, the effects of this Gratitude Festival are real.