The fourth-season finale of Dexter, originally aired on December 13, 2009, is “The Getaway.” It is the 12th episode of season 4 and the 48th episode of the series overall.
The episode concludes the season-long storyline involving Arthur Mitchell, the serial killer known as the Trinity Killer and played by John Lithgow. Dexter races to stop Arthur while Miami Metro’s investigation closes in, and Debra continues uncovering information about both Trinity and her own family history.
“The Getaway” is especially remembered for its final twist, which dramatically changes Dexter’s domestic life and sets the direction for the next season. Producers took unusual measures to protect the ending, including fake scripts and strict confidentiality rules.
Viewers sometimes confuse the finale with “Hello, Dexter Morgan,” the penultimate episode, or “My Bad,” which is the season 4 premiere. The date and episode number make “The Getaway” the single canonical answer.