Featuring two of the more memorable performances of the year, the drama “Appropriate Adult” (9 p.m., Sundance) offer viewers an unflinching and unforgettable study of human evil. “Adult” is a co-production between Sundance and Britain’s ITV Studios.

In the British justice system, an accused person considered mentally challenged or emotionally vulnerable is assigned an “appropriate adult,” someone to explain procedure and advocate for them throughout the legal process. In 1994, Janet Leach (Emily Watson), a modest mother of five, was assigned to Frederick West (Dominic West), then under scrutiny in the disappearance of his daughter.

Dominic West (“The Wire”) portrays Fred West with a bland self-assurance that straddles the line between arrogance and simple-mindedness. Over several interviews, conducted with perfunctory, clock-watching precision, he opens up to Leach as he never would to prosecutors, police or even his own attorney. And as he grows more comfortable, the confessions spill out of him with a chilling nonchalance. Killers, particularly serial killers, are often portrayed as supervillains and depraved eccentrics. Think Hannibal Lecter. But West emerges as stunningly normal and at the same time cunning, vulnerable and even seductive.

A harried unmarried mother with a live-in partner suffering from bipolar disorder, Leach endures West’s torrent of confessions with stoicism, but cannot hide the fact that she’s invited pure evil to enter her life, if not her heart. Her son and medicated partner can see what she cannot. And when West’s confessions of multiple murders hit the press, Leach becomes a minor celebrity, a lurid role she cannot perform without fumbling.

“Adult” explores the very nature of human depravity without ever depicting a single act of violence or displaying any victims. But West’s casual descriptions of his actions, delivered without emotion or remorse, are as haunting as any killing ever depicted on screen.

Tonight’s other highlights

• Outcasts prove their mettle in the 1964 special “Rudolph the Red-Nosed Reindeer” (7 p.m., CBS).

• Bob Costas hosts “The American Giving Awards” (7 p.m., NBC).

• Zachary Levi hosts the “2011 Video Game Awards” (7 p.m., Spike).

• More reindeer games on “The Flight Before Christmas” (8 p.m., CBS), from 2008.

• Republican candidates for president debate (8 p.m., ABC).

• The team feels overburdened by events on “Primeval” (8 p.m., BBC America).

• A decorative snow globe becomes endowed with awesome powers in the 2011 shocker “Snowmageddon” (8 p.m., Syfy).

• Antonio Banderas, Salma Hayek, Jimmy Carr and Coldplay appear on “The Graham Norton Show” (9 p.m., BBC America).

• Alan Cumming, Scott Adsit, Dave Hill and Faith Salie play along on “Would You Rather? With Graham Norton” (10 p.m., BBC America).

• Katy Perry hosts “Saturday Night Live” (10:30 p.m., NBC), featuring musical guest Robyn.