This season begins with Dexter living his new life, as a father. He has to adjust to life with a baby, which disrupts his work. He sings his infant baby, Harrison, a lullaby while looking at photos of a crime scene. He has to squeeze in time for his wife and baby in between work and his murders. His life is contrasted with the life of the "Trinity Killer", a killer that kills in sets of 3. The Trinity Killer is a very smart and experienced serial killer who is very good at killing without leaving a trace of evidence, even with leaving the body of the victim at the crime scene. This interests Dexter, since he always disposes of his victim's bodies.
Special Agent Lundy has returned to help try and catch the "Trinity Killer". This puts stress on Deb and Anton's relationship, because of her past relationship with him. A secret relationship between Batista and Laguerta begins.
Dexter is having a difficult time adjusting to his new role as a Dad with everything else going on. He has not been getting much sleep, and his insomnia has affected his work and his hunting. Dexter sets up for a killing in the boxing ring in an abandoned gym. He was waiting for one of his victims outside a club, and he falls asleep, missing his chance. At the end of the episode, with the remains of one of his victims in the trunk of his car, he falls asleep at the wheel, and crashes his car.