The film begins with the last few scenes of the
original film, where Laurie (Jamie Lee Curtis) sends
the two kids she's babysitting (Brian Andrews, Kyle
Richards) to run and get help after the home has been
invaded by psychopath Michael Myers (Dick Warlock). After the kids run off screaming, she is attacked by
Myers again, and is rescued when Dr. Sam Loomis
(Donald Pleasance) arrives and shoot Myers off of the upstairs balcony.
From here, the film is entirely new. Loomis rushes
out to the lawn and finds that Myers has vanished,
leaving behind only a bloody imprint in the grass. He
instructs a neighbor to phone the news to the police
and runs off in search of Myers again. Myers, aka The
Shape, lurks in the alleys nearby, watching Dr. Loomis
from a distance. Loomis meets up with Sherrif Leigh
Brackett (Charles Cyphers) and they drive off in
another direction in search of Myers. Myers then
steals a kitchen knife from a neighbor woman (Lucille
Benson). Down the street, Myers sees a young girl by the name of Alice (Anne Bruner) outside and stalks her. Inside, Alice is speaking on the phone with a friend who informs her that someone was murdered in Haddonfield. Alice switches on the radio and is shocked at the news when suddenly, the back door creaks open. Afraid, Alice ventures into the living room where Myers jumps out and thrusts the kitchen knife into her chest, causing blood to spurt up onto her neck.
Paramedics arrive at the Doyle house and take Laurie away on a stretcher.
She appears to be in shock, and she begs them not to
put her to sleep. The two EMTs are Budd (Leo Rossi)
and Jimmy (Lance Guest). Jimmy is younger and takes
an immediate interest in Laurie, concerned and
obviously distressed that someone close to him in age
has been attacked in Haddonfield. They take her to
Haddonfield Memorial Hospital, where she is tended to
by Dr. Mixter (Ford Rainey), head nurse Mrs. Alves
(Gloria Gifford), and RN Jill (Tawny Moyer).
Loomis and Brackett circle the neighborhood and happen
upon a young man wearing a white mask similar to the
one worn by Myers. In a freak accident, they pursue
him but an approaching patrol car crashes into him and
then into the side of a van. The violent explosion
incinerates the body. One of the approaching
patrolmen, Deputy Hunt (Hunter von Leer), has come to
tell Brackett the bad news that his daughter is among
the dead that have been discovered in the wake of
Myers's rampage. They drive off to the location so
that Brackett can identify her. Brackett, in shock at
finding his daughter dead, blames Loomis for allowing
Myers to escape and departs, leaving Hunt in charge. Loomis convinces Hunt that Michael Myers could
possibly still be alive, since they are uncertain who
exactly was struck and killed by the patrol car.
Another young nurse, Karen (Pamela Susan Shoop)
arrives at the hospital after staying too late at a
Halloween party. She is sharply reprimanded by Mrs.
Alves, even as they are both unaware that Michael
Myers is lurking in the hospital, watching them--Myers
has overheard a radio broadcast announcing that Laurie
was taken to the hospital, and has followed her here. Jimmy schemes to be alone with Laurie, both to console
her and get closer to her. He reveals to her that the
crazy man who was pursuing her earlier was Michael
Myers, who escaped from the mental hospital the
previous night. Laurie is confused and does not
understand why she seems to have been targeted by
Myers. Mrs. Alves interrupts and sends Jimmy away,
then discovers that the phones are suddenly out of
service. The security guard, Mr. Garrett (Cliff
Emmich), explores the basement and rear of the
hospital to search for the trouble and after he searches one of the closets, Michael suddenly leaps out and kills him by bashing him over the head with the back of a hammer. Mr. Garrett's death goes unnoticed despite the presence of a
nursing assistant named Janet (Ana Alicia).
Loomis and Hunt investigate a break in at the local
elementary school and find that Myers has been there;
a child's drawing of a family has a butcher knife
sticking in the image of the sister, and the word
"Samhain" has been scrawled in blood on the chalk
board. Loomis remarks on the Celtic origins of the
word, and he is surprised when Marion Chambers (Nancy
Stephens) approaches him. Chambers, who was with
Loomis the previous night when Myers made his escape,
has been sent with a Marshal (John Zenda) to return
Loomis to Haddonfield, on orders from the governor. Loomis is forcibly taken away, while Hunt promises to
find Myers.
Myers continues to murder the staff at the hospital. Budd and Karen attempt to make love in a hospital therapy pool,
but Myers turns up the temperature until Budd gets out
to check it. After strangling Budd to death, he
approaches Karen from behind and seizes her, holding
her under the scalding hot water until she drowns, the
flesh peeled away from her face.
Laurie has a reaction to her medication and goes into
shock, and when Janet goes to get Dr. Mixter, she finds
him dead in his private office, a needle thrust into
one eyeball. Myers appears behind Janet and grabs
her, thrusting another needle into her temple until
she, too, falls down dead.
Jimmy goes off to find help when nobody returns, and
Jill is summoned by another patient. While she is
gone, Myers enters Laurie's room at stabs at her bed,
but she is gone. When Jill returns, she finds the
room empty. Hindered by a cracked ankle and dazed
from the drugs, Laurie limps through the now-quiet
halls of the hospital, looking for a safe place to
hide.
Jimmy reappears and sends Jill off to get help, telling her to drive into town and bring back the police. But after she leaves, he finds the body of Mrs. Alves tied to a table, an IV tube in her arm having drained all of her blood out onto the floor. Suddenly he panics and tries to run, but he slips in the blood and falls on his back, slamming his head down on the floor, rendering him unconscious.
Jill finds all of the cars in the parking lot disabled, the tires slashed and the engines tampered with. After she runs back into the hospital, she sees Laurie in a hallway and tries to reach her, but Myers appears and kills her with a scalpel in her back. Laurie witnesses it and is terrified into action; she runs through the halls with Myers in pursuit. Rushing down a stairwell and into the basement, Laurie corners herself in a boiler room and must climb through a small window near the ceiling to escape, Myers almost slashing her ankles. After nearly cornering her again in an elevator, Laurie escapes and rushes into the parking lot, hiding in a parked car.
In the Marshal's car, Marion has a discussion with Dr. Loomis where she reveals information that he did not previously know; Laurie Strode is actually the sister of Michael Myers, born two years before Michael's original crime and adopted after the death of the parents two years after. Loomis immediately understands that Michael is after Laurie for a reason and commandeers the Marshal's car, pulling a gun on him and forcing him to make for the hospital.
In the parking lot of the hospital, Laurie sees a dark shape open the car door and get inside--it is Jimmy. He tries to start the car and cannot; Laurie tries to talk to him but he falls over the wheel again, passed out. The horn goes off and Laurie panics again, her hiding place revealed. She tries to leave the car and falls in the parking lot, still dazed. As she lays there, the Marshal's car pulls up and Loomis, Marion, and the Marshal get out and go into the hospital. Laurie cannot cry out until it's too late and they are inside, pulling the doors shut behind them.
As she gets to her feet, Myers appears across the parking lot, walking slowly toward her. Laurie runs to the doors and bangs on them, screaming, and attracts the attention of the others. They let her inside and Myers walks right through the closed glass doors. Loomis shoots him with his gun and he falls over, seemingly dead. After sending Marion out to the Marshal's car to use the radio for summoning the police, Loomis turns to comfort Laurie. Myers rises up again and slits the Marshal's throat with a scalpel, chasing Loomis and Laurie deeper into the hospital.
They corner themselves in an operating room. As Myers breaks down the door, Loomis gives Laurie his gun, which only has two shots left in it. When Myers gets in, he stabs Loomis in the stomach. Loomis falls over, mortally wounded. Laurie tries to stop Michael by calling his name, but he advances on her and she shoots him in the eyes. Blinded, he starts swinging his scalpel wildly. Loomis struggles to his feet and begins releasing oxygen into the room from the many tanks on the walls. Laurie follows suit until the doctor tells her to run. She bolts from the room and runs down the hall as Loomis ignites his cigarette lighter, causing a huge explosion. Even from the inferno, Myers emerges and keeps walking toward Laurie, until the flames consume him and he falls.
As the sky lightens into morning, Laurie is taken outside the hospital and placed into the back of an ambulance, as reporters, authorities and other onlookers watch. She stares blankly as the ambulance pulls away, seemingly in shock, but alive.