Season 4

Arthur Mitchell

Season 4 of Dexter is widely regarded as one of the best in the series, featuring Arthur Mitchell, aka The Trinity Killer, played by John Lithgow. This season explores Dexter's struggles to balance his new life as a husband and father while continuing his secret killings.

Dexter's New Life & Challenges

Dexter is now married to Rita Bennett and adjusting to life as a father to their newborn son, Harrison. However, family responsibilities make it harder for him to maintain his double life. He's sleep-deprived, struggling to focus, and makes dangerous mistakes, even passing out while hunting a target.

Meanwhile, Miami Metro is investigating a new serial killer: The Trinity Killer, a man who has eluded capture for decades. Trinity follows a ritualistic cycle, killing three victims in a specific order—first a young woman, then a father of two, and finally a mother who dies by suicide.

Arthur Mitchell – The Trinity Killer

Dexter soon discovers that Trinity is not just a ruthless killer but also a devoted family man, seemingly living a normal suburban life. Intrigued, Dexter infiltrates his world under the alias "Kyle Butler," hoping to learn how Arthur balances family and murder. However, Dexter soon realizes that Arthur is an abusive psychopath, terrorizing his wife and children.

As Dexter investigates further, he discovers the true meaning behind Trinity's pattern—as a child, Arthur accidentally caused the deaths of his own family members, and he has been recreating the tragedy ever since.

Tensions Escalate

• Debra learns the truth about Dexter's mother, leading her closer to his secret.
• Detective Frank Lundy returns, still obsessed with catching Trinity, but is murdered—initially suspected to be Trinity's doing.
• Arthur grows suspicious of Dexter, leading to an intense cat-and-mouse game.

Final Confrontation & Tragic Ending

Realizing Trinity is too dangerous to be left alive, Dexter finally captures and kills him. However, in a devastating twist, he returns home to find Rita murdered in the bathtub, with baby Harrison crying in a pool of blood—mirroring Dexter's own childhood trauma.

Season Conclusion

The season ends with Dexter holding Harrison, realizing that, despite all his efforts, he has failed to keep his family safe. Rita's death marks a turning point, as Dexter is left shattered and questioning everything.