The situation developed as follows:
Dexter targets a kill. He wants to get back to basics, and that means a new body for his table. Dexter hunts down an Internet predator and appears on the verge of a by-the-numbers murder, clean and simple. But before Dexter can kill his quarry, he gets a message from someone he thought had high-tailed it out of town—the vengeance-crazed abuse victim, Lumen Pierce. He drops the unconscious Internet predator, wrapped in plastic and ready for the killing, in his trunk and dashes to help Lumen.
Only to find Lumen's shot a man who, still alive, has crawled away. In a Miami warehouse, Dexter and Lumen bicker as Dexter tries to follow the blood trail of the man Lumen shot. He had, up until now, thought she was safely back in Minneapolis, but vengeance is still her modus operandi. She had found one of her abusers, she thought. "I didn't think it would be so hard to kill someone," Lumen confesses.
And then, of course, the police are on their way. Dexter hears from his colleagues that there's a homicide alert. Gunshots reported. He sees the warehouse address and looks genuinely panicked as he realizes, "Isn't that...here?" Fifteen minutes before Miami's homicide cops arrive at the warehouse.
The tension is magnetic as Dexter and Lumen scramble to find the runaway body. They do track down the bleeding victim soon enough, at least Dexter quickly processes a half dozen complications, including a call from his "Irish super-hero nanny" and initial doubts about whether this man, a trembling dentist, is actually one of the men who raped and tortured Lumen. "You don't have any proof!" he tells her. "I'm the proof!" Lumen fires back. "My memories, my experience." The stakes feel authentic.
Dexter plans to tend to the dentist's wounds until they overhear a phone call he makes: "She's alive ... that last fucking bitch is alive!" Dexter and Lumen approach him with poise, his guilt suddenly confirmed. In a nice touch, Dexter repeats baby Harrison's first mispronounced words of "die-die" as he breaks the man's neck. Lumen's mission of vengeance has now officially become Dexter's, too.
One final wild turn: the unconscious guy in Dex's trunk escapes right as Dexter had hoped to remove the new murder victim. Dexter jogs after the fleeing plastic-wrapped Internet predator while his sister Debra and Masuka scout the location as part of the homicide alert. The police are just around the corner. At the final, heart-pounding second, Dexter drags the Internet predator away from the police and chokes him with the plastic wrap.
The solution? Dexter pops out of the warehouse, now dressed in his standard forensics clothing. "You will not believe what I've found," he tells Deb and Masuka.
Inside: the two dead bodies face each other in what appears to be a lover's quarrel gone wrong. To the perverted Masuka, everything about the scene, from the plastic to the sexual possibilities of the warehouse components, makes complete sense. "Two words," says the short forensics expert with a smile as he eyes the bodies, "Auto-erotic mummification." Dexter predicts an easy case closed as Masuka begins describing asphyxiation and acting out the sexual moves.
Compartmentalization began as an architectural theory, Dexter muses in this week's episode. Life can also be divided into closed-off sections. Makes everything much simpler. If only. The episode begins with Dexter trying to right past mistakes, to keep his life neat and well-ordered—the blood slides over here, the police work there, and being a father? That whenever there's time. But our serial killer quickly realizes, in an episode more dynamic and fun than many in recent weeks, that compartmentalization is a dream. Lumen happened.