Once More, With Feeling
Things begin with Buffy, Willow, Tara and Dawn preparing for a regular day. After their waking ritual, the gang resumes their typical activities at the Magic Box. It seems to be the same old song.
That night, Buffy patrols. Troubled, the Slayer begins singing about being the Slayer. Suddenly, she is attacked by vamp. Without missing a note, she dusts him. Moving on, she comes across two more vamps and a demon, who are ritually sacrificing a man. She grabs the demon's sword, dusts one vamp and then fatally stabs the demon. Buffy saves the man and then dusts the last vamp.
The next day, an uncertain Buffy asks the gang if they broke into song the previous night. As it turns out, everyone did. Without warning, "The Ripper" himself instigates a number about the cause of the musical spell. The song ends as the gang discovers that the entire town is singing and dancing.
After school, Dawn joins in and shares that a song broke out in her math class. While no one is looking, she steals a talisman off of the counter. Citing that they have a book that could explain the phenomenon, Tara and Willow leave the rest of the gang. The two take a shortcut home through a park and Tara bursts into a song about being under Willow’s spell.
Right after they wake up, Anya and Xander begin singing and dancing. Revealing their true feelings, the two sing about each other’s little perks. Finishing their number, they collapse on the couch and begin laughing.
That night, at Spike's crypt, Buffy and the vamp talk about the spell. Suddenly, Spike breaks into a song about his love for Buffy and her unwillingness to return his affection. Horrified, Buffy runs away.
At Buffy's house, Dawn accidentally rants about the Halloween fight between Willow and Tara. Not remembering a fight, Tara rushes out of the house. Quietly, Dawn begins singing only to be cut short by some evil puppets.
Later, at the Bronze, Dawn wakes up. While dancing, she tries to escape and is surrounded by puppet men. Then, a demon, Sweet, appears and informs Dawn that she summoned him and must become his queen. After finding out that the Slayer is Dawn's sister, the demon orders his henchmen to find Buffy and tell her that he has Dawn.
While sparring with Buffy, Giles breaks into song. Meanwhile, in the front room, Xander, Anya and Willow work as Tara enters. Musically, Tara confronts Willow about her evildoing as Giles explains to Buffy why he is leaving. After the song, Spike busts in with one of the puppet men—who tells everyone that Sweet has kidnapped Dawn. After the puppet escapes, Giles insists that the gang let Buffy go alone on the mission.
In unison, the Demon and all of the Scoobs begin singing from different locations. Everyone seems to be worried. As the song concludes, Buffy kicks open the door to the Bronze ready for battle. As singing commences between Buffy and the demon, the rest of the gang shows up. Carelessly, Buffy reveals her trip to Heaven and then begins dancing out of control. Still angry with her, Spike holds her so that she doesn't explode. Things wind down and the demon informs the Scoobs that he must take Dawn because she summoned him with the talisman. To Sweet’s chagrin, we find out that Xander actually summoned the sharp-dressed monster. After one last verse, the demon leaves them all with a final note about being truthful.
The gang breaks into one final song asking the question, "where do we go from here?" Angry, Spike leaves the Bronze, only to be followed by Buffy. The two break into a reprise of their previous song and the vamp and the Slayer lock lips in a long passionate kiss.
Summary from Buffy.com