New York, 1977: Spike is fighting Nikki Wood, a Slayer also seen in the fifth season episode "Fool for Love", in a park at night in pouring rain while her son watches from his hiding place behind a bench. Spike has the opportunity to kill her but the kid distracts him and he lets her go with the promise that they'll meet again. "Love the coat," he adds with a smile, before he leaves. When he's gone, a clearly troubled Nikki finds her son and calms his fears by telling him, "The mission is what matters."
The scene switches to an alley in present-day Sunnydale. Buffy, Principal Robin Wood, and Spike are fighting a bunch of vampires. Buffy and Spike manage to kill their quarry, but a vampire has knocked Wood to the ground, and is about to kill him. Spike saves Wood by killing the vampire from behind, then helps him up. Wood thanks him, but the camera zooms in on the stake he's holding and there is blood dripping from his hand. He still seems to be determined to have his revenge.
Previously, the First Evil had programmed Spike with a post-hypnotic suggestion in his mind that allows it to turn Spike violent using an old song, "Early One Morning", as a trigger. This way the First was able to command him to kill again. Buffy wants to find out how to turn it off so that she can fully trust Spike against the First, but Giles opposes Buffy. In his opinion, Spike is dangerous and must be contained or disposed of.
With all that happening the Scoobies go to the basement of Buffy's house, where Willow makes a spell with the Prokaryote stone, a magical artifact that penetrates Spike's mind and makes him more conscious of how the trigger works. In this way, we learn about his human past as William, about his sick mother and how he turned her into a vampire only to be cruelly rejected by her newly vampiric self. The song that his mother used to sing makes him relive the whole episode and switch into his evil, soulless self. He unwittingly hurts Dawn in the process and scares them all, except Buffy. Meanwhile, Willow receives a phone call from a girl named Fred and quickly leaves for Los Angeles. She apologizes to Buffy for her quick departure, but promises to be back as soon as she can, and she may even return with good news.
After the previous incident, Wood privately convinces Giles that Spike must die. Giles learns that Wood is the son of Nikki, a Slayer now dead, and that Spike murdered her. After a brief chat they make a plan. Giles is to distract Buffy while Wood takes care of Spike. Giles takes Buffy on patrol and begins asking her indirect questions and making obscure references to her role against the First.
In the meantime, Wood takes Spike to his hideout with the promise to protect him, but this feeling is clearly undermined as soon as they enter and it is revealed that the walls are covered with crosses. Wood reveals to Spike that he knows he murdered his mother and that he's going to kill the monster inside him. Spike says he has no remorse over killing Wood's mother, and that it was "all part of the game". Wood then goes to his computer and starts "Early One Morning" in iTunes. This triggers Spike's violent, monstrous self and the two fight. As the fight progresses, Spike continues to relive the events that transpired between him and his mother on a more conscious level, due to the Prokaryote Stone. Wood takes advantage of Spike's flashbacks, and using weapons, knocks Spike around until he cannot stand and he then attempts to stake him. Spike regains control of his own mind, having faced his own anger and regret on turning his mother into a vampire and then being forced to kill her. Spike easily defeats Wood and demonstrates that the song has no more power over him, and tells Wood that the difference between his mother and Spike's mother, is that Spike's mother actually loved him back. (Referring to a previous comment he made that Wood's mother did not love him enough to give up the Slayer duties), and sinks his teeth into Wood's neck.
All the while, Buffy had been fighting a vampire at the cemetery and talking to Giles, when she suddenly realizes that Giles is trying to distract her while Wood kills Spike. She kills the vampire, leaves Giles and rushes to Wood's place. Buffy finds Spike at Wood's place, with Wood badly beaten, but alive. Spike tells her that he spared Wood out of respect for his mother, but if Wood tries anything again, he'll kill him. Buffy goes inside, and tells him that she needs Spike alive and that she has no time for personal vendettas. She promises him that if he tries anything like this again, she'll let Spike kill him. "The mission is what matters," she says firmly, and Wood winces to hear his mother's words repeated all over again, by a different Slayer.
Once at home, Buffy tells Giles that his and Wood's plan failed. In spite of that, he tries to pick up from where they left off earlier, and continue the interrupted lesson. But Buffy says icily that she already knows everything he can teach her. And with that, she closes the door in his face.