Casting against type works in ‘SVU’ case

When it’s done right, contrarian casting can add an intangible thrill to the TV drama, an unexpected ingredient that enlivens the formula.

Think of John Larroquette, the “Night Court” buffoon, and Henry Winkler, Fonzie from “Happy Days,” in their disquieting turns on “The Practice,” or Neil Patrick Harris, fresh-faced “Doogie Howser, M.D.” himself, as a seedy suspect on “Homicide: Life on the Street.”

The latest evidence comes in tonight’s episode of “Law & Order: Special Victims Unit” (10 p.m., NBC), featuring a startling performance by Fred Savage, the former teenage star of “The Wonder Years,” as a suspected serial rapist with a “Who, me?” demeanor.

The episode also showcases the unrelentingly strong work of co-star Mariska Hargitay as Det. Benson, the squad’s hard-nosed but empathetic conscience, and delves into one of the show’s most potent recurring themes: the further victimization of crime victims.

After arresting Savage’s character in the attacks on several neighborhood women, Benson and Stabler (Christopher Meloni) struggle to obtain an indictment of their suspect with the help of a terrified, reluctant eyewitness -- his last victim.

When the case eventually goes to trial, the defendant’s decision to act as his own lawyer throws the outcome into doubt, as he proves to be a formidable foe for Asst. Dist. Atty. Cabot (Stephanie March). Feigning nervous innocence, he seems to score legal points and jury sympathy with every shrug.

Meanwhile, with the defendant free on bail, his victims are subject to stalking and intimidation, all the more so when they must sacrifice their privacy to obtain a protective order against him.

The legal wrangling prompts a crisis of faith for Benson, who eventually pulls a maneuver that puts her at odds with a rape crisis counselor involved in the case.

In a satisfying last twist, the show coolly revisits another favorite theme of the series: moral vengeance.