The Lost Boys starts when Michael Emerson, together with his younger brother, Sam, and their mother, Lucy, go to Santa Carla, California to live with their grandfather.
As soon as they get into town, the brothers start spending most of their time in a place called the Boardwalk. Meanwhile, their mother begins working for the local video stored owned by a man who calls himself Max. While hanging out on the Boardwalk, a girl named Star catches Michael’s attention. Sam, on the other hand, becomes friends with Edgar and Alan Frog who consider themselves as vampire hunters.
When Michael tries to befriend Star, her boyfriend David butts in and instead leads Michael down the beach where Michael almost falls off from a cliff. Afterwards, David invites Michael to join his group and they head to the group’s hideout beneath the cliff. David offers Michael a glass of wine which Star dissuades him from drinking, claiming that the glass contains blood. However, Michael still drinks the liquid and before the night ends, he falls off a valley near the train tracks.
Michael wakes up thirsting for blood. When he attempts to satiate his thirst with the blood of Sam’s dog, the dog fights him off and bites him in the hand. After the event, Sam sees that Michael does not have any reflection on the mirror. Realizing that his brother has become a vampire, Sam runs away from his brother. His brother tries to make him understand what has happened to him but Sam pays him no heed. Left with no choice, Michael goes to his own room and starts exploring his new abilities. It also dawns on him that he is slowly becoming a vampire. Meanwhile, Sam learns that Michael’s transformation is still incomplete since he has not killed anybody yet. Sam then seeks his friends’ help in trying to find out the vampires’ leader. They are all convinced that the store owner Max is the vampire leader but they realize that it is not true.
When Michael meets David again, the latter tries to persuade him to kill people for blood. However, Michael is appalled by the sight of people getting killed so he ends up running back to their home. There, Star comes to him and confesses that she’s just like him and she searches for something that can cure their condition. Together with Sam and his friends, Michael sneaks into David and his gang’s lair. They manage to kill a vampire with a stake but the commotion wakes David and the other vampire. The group barely escape, tagging along with them Star and another half-vampire, Laddie.
In their house, Michael and Sam, prepare together with their friends for the vampires’ attack. As the vampires rush in their house, they are able to finish some of their enemies using a variety of tools like holy water and garlic. Michael beats David and kills him but to their disappointment, he, Star, and Laddie do no return to their normal selves. Then, Lucy comes home with Max and it is revealed that he is really the head of the vampire cove. They also learn that he intends to make Lucy his bride and the mother of his descendants. Just as Max is about to turn Lucy, Michael and Sam’s breaks through the wall using his jeep. The vehicles hits Max and he gets impaled with one of the posts. At that point, Michael, Star, and Laddie become humans again.
The movie ends with the old man getting a drink from the refrigerator and making casual comments on how he hates the vampires in Santa Carla.