The protagonist of the film Next Obsesion (The Boy Next Door) is a woman who has a son and who has just moved. He has divorced and therefore has changed his house, to change his environment and start a new life.
She works as a teacher and it happens that one of her students, a boy, is his neighbor. Little by little it becomes related to him, so much so that in the end both begin a relationship that should not have.
Both have a big difference in age and he is also their student, so if the relationship comes to light could have both legal and work problems, although he realizes that there is something much worse.
The boy, who looked like a good person, is dangerous and obsessive, so much so that the teacher realizes that his life is in danger, and what is worse, so is that of his son.