After a training session in the mansion, Buffy and Angel get a little too close for comfort. With her eighteenth birthday almost upon her, Buffy is anxiously awaiting to spend some time with her father at an ice show. Later, at the library, Giles leads Buffy through a study of vibratory stones. Despite being a little fidgety, Buffy manages to concentrate on one of the stones. Afterwards, Buffy battles with a vampire in the park. Just as she is about to deliver the final blow, something surges through Buffy's body, and she suddenly finds herself powerless. The vampire quickly takes the upper hand, knocking her to the ground and turning the wooden stake on the Slayer herself. Buffy panicks, but she is still able to stun the vampire with a headbutt and push him off of her. She grabs the stake and aims it straight up as the vampire leaps onto her. In an instant, the vampire is nothing but dust.

Giles enters the library the next morning to find Buffy practicing her aim with throwing knives. As the random placing of the knives on and around the target shows, the Slayer is not herself. Giles ensures Buffy that she'll be okay. Outside, Buffy downplays her friends' enthusiasm over the upcoming birthday, suggesting that a party may not be the greatest of ideas, given her tainted history with such social gatherings. Later that night, Buffy notices a birthday balloon floating in her kitchen with what appear to be an envelope and tickets attached to the string. As Joyce informs her that Hank won't be able to free up enough time to take her to the ice show, Buffy folds up the envelope without even opening it. Meanwhile, three men are hard at work inside an old, abandoned boarding house. One of the men, Quentin Travers, looks on as his two associates, Blair and Hobson, work on laying bricks in several of the doorways. At the library, Buffy tries to indirectly ask Giles to take her to the ice show, but he is more interested in making her study the vibratory stones. After Buffy finally gives up her futile effort, Giles instructs her to concentrate on the fault inside the large blue stone. As Buffy stares at it, she suddenly loses all touch with the outside world. Giles checks to make sure Buffy's in a trance, then takes an injection kit out of his bag. He injects a strange, green fluid into Buffy's arm. After he finishes the task and puts away the kit, Giles waves his hand in front of the fault, breaking Buffy's trance. Unaware of what just happened, Buffy decides to call it a night and leaves Giles alone in the library.

Outside of school the next morning, Buffy notices a guy harassing Cordelia. Buffy walks up to the guy and grabs him by the arm. However, she suddenly realizes that she doesn't have enough strength to do anything to the guy, who casually shoves her to the ground with that one arm. Buffy finds Giles in the hallway and tells him about her disturbing loss of strength. Giles doesn't show a great deal of concern, although he definitely knows why Buffy is going through this. Giles speaks with Quentin at the boarding house, voicing his disagreement with the Watcher Council's insistence on subjecting Buffy to the Cruciamentum. The Cruciamentum is a test which all Slayers must endure when they reach the age of eighteen in order to prove their instinctual skills and resourcefulness. To do so, the Slayer must survive an encounter with a vicious vampire while trapped inside a small space. In this case, Buffy must defeat an insane vampire, Zackary Kralik, in the confines of this boarding house. After Giles leaves, a loud, painful scream emanates from Kralik's coffin. Blair and Hobson open the coffin and give Kralik his pills. Giles returns to the library, where Buffy, Willow, Xander, and Oz try to find any relevant info in the books that might explain her loss of power. While Buffy continues to search for answers, Kralik's screaming keeps Blair and Hobson from getting any rest. While Hobson takes a break, Blair opens the coffin to learn that Kralik wants more pills. As Blair goes to the kitchen to fill the glass with water, Kralik screams to cover up the sound of his straightjacket ripping at the seams. Kralik then tricks Blair into stepping close to the coffin and grabs him by the throat with his freed arm before sinking his fangs into his neck. At the mansion, Angel gives a book of poetry to Buffy for her birthday. Unfortunately, Buffy is distracted by her power loss to fully appreciate Angel's gift. Buffy fears that she may have lost what made her special. Angel consoles her by confessing that he watched her long before she moved to Sunnydale, admitting that he loved her then every bit as much as he does now. Meanwhile, Blair rises in front of Kralik as a newly-turned vampire. He picks up an axe and frees Kralik from his restraints.

Giles stops by the boarding house to check in on things, but nobody seems to be around. After noticing blood on the stairway railing, Giles grabs a make-shift stake and opens Kralik's tomb. Finding it empty, Giles goes to the kitchen and discovers Hobson's dead corpse. Overcome by the grotesque sight and smell, Giles runs out of the house. He needs to find Buffy, who is walking the streets alone. She runs into Kralik, who grabs her jacket. Unable to fight him as she normally would, Buffy turns and runs for her life. She tries to climb over, then under a fence. Blair shows up and tries to pull her back, but Buffy escapes and runs out into the middle of the street. Giles arrives just in time, and Buffy jumps into his car. Back at the library, Giles tells the whole truth to Buffy, showing her the syringe filled with an organic compound of muscle relaxants and adrenal suppressers. He informs her that the effects of the compound will wear off in a few days, but Buffy is too furious to care about that right now. Giles goes on to tell her that he just invalidated the test by telling her about it ahead of time. Unfortunately, Buffy refuses to listen or forgive him. As soon as Cordelia walks into the library to do some research for a paper, Buffy asks her for a ride home. While Cordelia drives Buffy home, Joyce hears a noise on her front porch. She goes out and sees Buffy's jacket draped over a figure. Assuming it's Buffy, she bends down towards the covered figure. However, it's not Buffy at all, but really Kralik. When Buffy arrives home, she finds a polaroid of her mother and Kralik. She packs a large amount of her slaying supplies into her bag and heads towards the mansion.

Tied to a chair and gagged, Joyce can do nothing but watch as Kralik takes countless polaroids of her while rambling about his hatred for mothers. Buffy walks in through the main entrance of the boarding house and looks around. As she realizes that all of the other exits have been sealed by bricks, Blair locks the main entrance, trapping the Slayer inside. Meanwhile, Quentin visits Giles at the library and tells him that the Cruciamentum has begun. Giles informs him that he disclosed all of the information concerning the test, but none of that matters right now. He leaves Quentin in the library and races towards the boarding house. Buffy encounters Kralik and tries to take him out with her crossbow, but it's no use. He chases Buffy through the house. She takes refuge inside a dark room. When she turns the light on, Buffy sees that the walls are completely plastered with photos of her helpless mother. She runs out of the room, and Kralik finally traps her in the hallway. Buffy attempts to ward him off with a cross, but Kralik is so insane that he actually enjoys the pain it causes. Before he can bite into her neck, Kralik is suddenly seized by his painful need to take his pills. He fishes the medicine bottle out of his pocket. Spotting an opportunity, Buffy grabs the bottle out of his hands and dives through a laundry chute. Landing in the basement, Buffy finds Joyce on the chair. When Kralik reaches the basement, Buffy tries to flee the scene with his pills. He rips the bottle out of her hands and quickly grabs the nearby glass of water. After swallowing the pills with the water, Kralik suddenly notices a burning sensation inside himself. Buffy holds out an empty bottle of Holy Water. The blessed water soon disintegrates Kralik. As Buffy works on freeing Joyce from the chair, both Giles and Blair crash into the basement. Giles finishes the vampire off, then leaves with Joyce and Buffy.

In the library, Quentin commends Buffy on her successful passing of the test. However, he has bad news for Giles. Since he has demonstrated a relationship with Buffy that the Council has deemed too close, like the way a father loves his daughter, Giles is relieved of his duties as Buffy's Watcher. Quentin then tells Buffy that she will be assigned a new Watcher soon. Struck by this revelation of how much Giles cares for her, Buffy calmly allows him to tend to her wounds. Back at home, Buffy's friends try to make sense of Giles' being fired... especially Willow, who almost refuses to believe the mere possibility of Giles losing his job.

~Episode Summary by: Alan Hufana