This story about a mass murderer shifts back and forth from the present to the past, as his mother, Eva (Tilda Swinton) remembers incidents with her family and troubled son, Kevin. It begins with her visiting him in prison--and they are both uncomfortable, neither speaking. She has also started a new, minimum salary job--which is at odds with her wealthy past life. How did she lose it all and why is she now such a wreck? We see how strange Kevin is when he's 6-8 years old and how he begins killing animals and injuring his younger sister when he's a teenager. Ultimately he takes his meanness out on his fellow students in a very cold, calculated and horrific way.
This is one of the better "realistic" serial killer movies I've seen in a long while. It's completely believable and Ezra Miller is completely believable as the teenaged Kevin. Highly recommended.