Frank Lundy was a high-ranking and illustrious FBI Special Agent; serving as one of their manhunters and the Bureau's top agent. Lundy was recruited by Cpt. Matthews to lead the task force dedicated to identifying and arresting the Bay Harbor Butcher.

Lundy was cool, calm, confident and incredibly intelligent and learned about the criminal mind, often finding the important case evidence the frustrated Miami PD normally overlooked. Lundy, himself, was infamous with police agencies due to him breaking impossible high-profile criminal cases (e.g. the real-life Green River Killer and the DC Sniper). On a personal level, he had a wife, who passed away due to cancer, and a daughter. Unknown to anyone else, Lundy had secretly devoted 15 years of his career to hunting down the "Trinity Killer", tracking him and seeing him as the most elusive serial killer he has ever encountered.

During the hunt for the Bay Harbor Butcher, Lundy became dangerously close to finding out Dexter is the Butcher he is seeking, and at the same time becomes involved in a relationship with Debra, helping her get over her left-over chaotic emotions from her time as the prisoner of the Ice Truck Killer. In the end, Dexter outmaneuvers and frames Doakes as the Butcher, leading Lundy to lead the entire police forces in a full-scale manhunt to find Doakes. After Doakes is killed in a seemingly accidental explosion, the case is considered closed and Lundy moves on to find another serial killer in Oregon.

Lundy retired from the FBI some time later, but continued his mission to hunting Trinity. After tracking him to Miami, Lundy, no longer possessing access to the full resources of the FBI, asked for Dexter's, and later Debra's, help in pursuing the Trinity Killer - and, eventually, it seemed Lundy was closing in on Trinity. In the process, Lundy and Debra rekindle their relationship. No sooner had they agreed to continue seeing each other, both Lundy and Debra were attacked and shot by an unseen gunman, who robbed them and left them to die. Lundy bled out and died from his injuries.

Dexter mourned Lundy's death; having seen him as a "worthy adversary" and felt he deserved a more fitting end. Debra, however, blames herself for what happened. It was originally believed the Vacation Murderers were responsible, but Dexter suspected Trinity. Debra's own investigation, however, reveals that neither the Vacation Murderers nor Trinity were the shooter. Quinn's girlfriend, Christine Hill, who was revealed to be a daughter of Trinity, was revealed to be the shooter.