They're catching killers. He's about to become one.

Dexter: Original Sin

In 1991 Miami, Dexter Morgan transitions from student to avenging serial killer. When his bloodthirsty urges can't be ignored any longer, Dexter must learn to channel his inner darkness. With the guidance of his father, Harry, he adopts a Code designed to help him find and kill people who deserve to be eliminated from society without getting on law enforcements' radar. This is a particular challenge for young Dexter as he begins a forensics internship at the Miami Metro Police Department.