The flu has been spreading around Sunnydale High, and Buffy's one of the unlucky souls who's got it. While on a routine patrol through the cemetery, Buffy runs into Xander, Willow, and Cordelia. Before she can get them to go home, Angel appears and attacks Cordy. Buffy fends him off, but the flu has made her too weak to fight him effectively. Angel nearly bites Buffy when the others come to her aid and thwart him back with their crosses. After Angel leaves, Buffy collapses and lies on the ground, unconscious.

The gang brings Buffy to the emergency room of Sunnydale General. Giles and Joyce soon arrive, and they wait for Buffy to be moved to another room so they could see her. On the way to room, Buffy realizes that she's going to be there awhile, so she tries to get out, screaming that she has to kill the vampires. Dr. Wilkinson injects a tranquilizer to calm her down. Soon, Buffy is asleep in her new room while the others wait outside in the hall. Joyce tells everyone that Buffy has been afraid of hospitals ever since she saw her cousin Celia die in a hospital when they were both very young. The group goes home while Xander stays behind to protect Buffy in case Angel shows up. That night, Buffy is still overcome with her fever when she notices a young boy standing in her doorway. As the boy walks away, Buffy sees a tall, demonic man following the boy. He is dressed in black clothes and a black hat, and his fingers are long and pointed. Buffy gets out of her bed to follow them, but she soon finds herself in a flashback to a time when she was much younger, walking down a similar hospital hallway. As her young self walks into a room and approaches the bed curtains, Buffy wakes up, realizing that she was just dreaming. She then gets out of bed and walks down the hall. She stops outside of a door from which a body of a recently diseased girl is being wheeled out of. Buffy eavesdrops on Dr. Wilkinson talking with another doctor, Dr. Stanley Backer. Dr. Wilkinson is arguing about some kind of experimental procedure that Dr. Backer has been performing on the children. Buffy then notices two children standing before her. One of them is the same boy she saw earlier, who tells her that Death is coming for them, and that he can't be seen by grownups. Elsewhere, Angel walks into the hospital, holding some flowers for Buffy. Xander blocks his path and challenges him to a fight, but Angel simply points out Xander's apparent jealousy of Angel for getting to Buffy first. Angel then turns around and leaves.

The next morning, Buffy's fever has gone down, and the gang pays her a visit. Buffy tells them about the apparent demon she saw walking the halls, the one that grownups can't see, but also notes that she may have just been delusional from her fever. She also tells them about the girl who died and Dr. Backer's experiments. Giles and Willow return to the library to do some research while Xander and Cordy snoop around the hospital for more info. They find nothing, so Xander decides to stay behind and watch after Buffy. Cordy is upset with him for his obvious attraction that he still holds for Buffy, but she later returns with donuts and coffee to keep Xander company. In the meantime, Giles and Willow concoct a theory that the kids think they're seeing Death, but they're really seeing Dr. Backer. Willow researches his background, but can't find much to convict him of anything. Later that night, Buffy sneaks out of her room again. She heads for the children's ward, where Dr. Backer is preparing to inject a sleeping girl with an unknown solution. He then hears something, but it is too late, for an invisible force attacks the doctor, slashing away at his body. The young boy, Ryan, wakes up and watches in horror as Dr. Backer is slashed to death by the demon. Buffy looks in and sees Dr. Backer being attacked, but she can't see the attacker. His lifeless body is then thrown out of the room, and before Buffy can reach it, she is knocked back by the unseen force. She lies against the wall, unconscious, while Dr. Backer's body is dragged down the hall and out of sight.

The next morning, Buffy tells the gang that Backer is no longer their suspect, then shows them a drawing that Ryan made of the demon. Joyce arrives and tells Buffy that she's been cleared to go home, but Buffy makes up an excuse that she's still not feeling well so she can stay in the hospital and fight the demon. Willow stays to help Buffy investigate Dr. Backer's office for clues as to why he was killed, while Xander elects to stand guard at the hospital. This leaves Giles to reluctantly work with Cordy in the library. In Dr. Backer's office, Willow finds a log proving that Backer was innoculating the kids with the same virus they were infected with in an attempt to raise their temperature and burn out their fever. According the log, the process was starting to work, so Backer really was helping the children all along. At the library, Cordy notices that a picture on the cover of a book resembles the picture that Ryan drew. She calls Buffy and tells them that the name of the demon is Der Kindestod. Giles then tells Buffy that Kindestod kills its victims by sitting on top of them and pinning them on their backs. It then sucks the life out of them somehow. Buffy suddenly has another flashback to her earlier years. The younger Buffy walks into the room and opens the curtains, only to see Celia screaming with her hands in front of her, as if she is trying to push some invisible object off of her. Buffy realizes that her cousin Celia was killed by Kindestod. After hanging up the phone, Buffy realizes that the only time she was able to see the Kindestod was when she was still under the effects of her fever. Willow and Buffy sneak into Backer's office again. Buffy opens the refrigerator and removes a test tube that contains the same virus strain that Backer was using in his experiments. Willow dilutes it with water before Buffy drinks it. Sick again, Buffy stumbles to the children's ward with Willow's help. However, all the children are no longer in their room. Buffy then sees Kindestod walking around inside the room, then entering a door labelled "Basement Access". The door is locked, so Buffy needs to find another way to the basement. Dr. Wilkinson walks into the hallway and tries to get Buffy back to her room, but Buffy pushes her away, and she and Willow run for it. Two security guards stop them, but Willow throws an imaginary fit to divert the guards while Buffy slips by. She finds Xander, and the two of them head down to the basement. They find Ryan pinned to the floor by Kindestod, while the rest of the children sit together screaming. Buffy fights Kindestod while Xander moves the others to safety. Before Kindestod can drain Buffy of her life force, she grabs his head with both hands and snaps his neck, killing him instantly.

The next morning, Buffy is back in the comfort of her own bedroom. Xander and Willow are also there, keeping her company while she recovers from her fever again. Joyce brings Buffy a letter that just arrived in the mail. It's from Ryan, and Buffy opens it to find a drawing of Buffy standing victoriously over the body of Kindestod, it's neck cracked open and blood spurting out.