Showtime

Dexter's strength comes from the primal majesty of its story lines, a strength beyond details that touches on bigger, viscerally psychological themes. The show provides broad strokes. Dexter finds a long-lost brother. Dexter breaks Harry's code. Dexter meets a best friend. Dexter gets married to longtime lover Rita. Despite the radical prospect of a serial-killer lead, the show has offered a classic set of obstacles: how to articulate emotion and loss, to connect with family, how to reconcile addiction, a wife and children, friendship and deception, isolation and love.

The fifth season of Dexter dramatizes the fallout of his wife Rita's death without always explicitly mentioning her. Here enters the character of blonde, embittered Lumen (Julia Stiles), who, as we've seen in recent weeks, has developed her own dark passenger that drives her to kill the men who beat and raped her and twelve other women. By this week's season finale, Lumen succeeded in killing all five of the abusers with the help of Dexter. Lumen marks a new honesty in Dexter's emotional development. He may have loved Rita, but his wife never suspected he sank knives into people. Lumen knew yet still cared for and practically worshipped Dexter. A genuinely tender romance developed between Dexter and Lumen this season, a slow chemistry evolving between two damaged personalities. Helping Lumen also allowed him to forget Rita, to transfer his guilt into action.

The brilliance of Dexter's fifth-season finale emerged in the raw and heartbreaking conclusion to this mismatched romance. Dexter again loses a loved one in this season's finale, but for a different reason than last year's. He cheerily approaches Lumen the morning after they kill her last abuser, Jordan Chase. Her tears interrupt his quips about breakfast foods. Her dark passenger, Dexter realizes, it's gone. She explains she needs to leave immediately.

"I can't do it any more," Lumen tells him, referring to the murder and double life that Dexter embodies. "What we've been doing."

"You don't have to." He begins to look visibly broken, his emotions not remotely an act.

"But you do. We both know that."

Dexter throws the plate he holds, shatters it, and the two devastated characters crouch on the floor. It's a moment of crushing, painful honesty reminiscent of the worst break-ups. Michael C. Hall and Julia Stiles deliver the scene completely and convincingly. Later, in the episode's final moments, Dexter's quiet acceptance of his own isolation (surrounded, it must be pointed out, by family and coworkers at his son's birthday party) is a damning reminder that he, on an internal level, still feels cut off from the world. Like a grotesque Pinocchio story, where wooden Pinocchio ached to be a real boy, the psychologically shut-off Dexter had experienced "the briefest chance to be human" with Lumen.

Those poignant scenes provide an anchor for the broad, big-picture themes of Dexter. They justify why fans love the show and understandably so. The underlying trauma is larger than life, with epic capacity as metaphor.

Dexter tends to botch the small details. A prime example is the lazy denouement of Quinn's Dexter-stalking and the murder of Liddy. So many elements pointed to trouble with this plotline all season: prim, obnoxious Quinn grows paranoid about Dexter, stalks him, hires another cop named Stan Liddy to investigate, and then, when Quinn falls in love with Dexter's sister, tries to call off the investigation to no avail.

But Dexter killed Liddy in a moment of passion, and signs pointed to Quinn. There was blood on Quinn's shoe, his name on surveillance registry, the record of calls between him and Liddy. In the finale, Quinn is dramatically called out and briefly put behind bars—a genuine and thrilling leap in the plot, it seemed. Because would he have to go public with the Dexter investigation? With the suspicion that Dexter may have killed Liddy? Yet he's loose by end of the episode, thanks to ... Dexter's blood work? Uh, wait. What? Yes, the drop of blood was suspicious but hardly the cops' only black mark against Quinn and likely not the last lead in Liddy's murder. If Quinn were truly investigated, the police would have found Liddy's photos of Dexter and Lumen in Quinn's apartment. They likely would have also found additional surveillance records in Liddy's place. Clearing Quinn on account of that one blood drop was a pat fix, a flirtation with consequence but too bashful to explore real trouble.

The same is true for Deb's discovery of Dexter and Lumen at Jordan Chase's murder scene. Her arrival heralds a familiar, nerve-wracking question: Will she finally—gasp—learn her brother's secret? (Attentive viewers probably haven't forgotten the writers played this same card with two other murder scenes this season—Deb also showed during the "auto-erotic mummification" incident and at the banker's house.) Conveniently, the show never had to face the tough dramatic questions because a gauzy sheet blocked Deb's view of her vigilante brother and Lumen. Debra offered strong bark but no bite, ultimately choosing to let them go. And, of course, she learned nothing of their identities.

Dexter has been renewed for a sixth season, and despite its frustrations, the show has more than enough promise to warrant attention. Unlike last year, no grand cliffhanger drives the coming episodes. Anything can happen, and a fresh start may be exactly what the upcoming season needs ... especially if the show will stop pulling punches and tighten loose ends. The arc of Lumen was largely a success—tender, generally well acted, resonant, and appropriate to our serial killer's larger evolution. It's the rest of Dexter that needs to follow through.