The women-behind-bars movie “Racing for Time” (8 p.m. today, Lifetime) adds a theme of redemption and uplift to a grim tale of juvenile prisoners.

The first third of the story introduces us to an angry crew of minor offenders. The rhythm of their lives settles into a dull procession of getting high and engaging in racial gang fights before an idealistic prison guard (Charles Dutton) suggests that the girls participate in a track program.

The rest of the film is as upbeat as it is predictable, with fights giving way to racing montages and pep talks from Dutton’s character and the other cynical prison officials that he brings to his side.

¢ Network viewers will find repeats of the Showtime drama “Dexter” (9 p.m. Sunday, CBS) to be either one of the best shows on television or the sickest and most sadistic – or both.

The remarkable Michael C. Hall (“Six Feet Under”) stars in the title role. He’s a forensics expert for the Miami police force whose specialty is blood splatter patterns. He’s the foster son of a celebrated officer (James Remar) and the stepbrother of Debra (Jennifer Carpenter), a struggling female officer.

He’s also a serial killer, a disturbed psychopath and completely devoid of human emotions. He fakes his way through normal interaction, bringing donuts to work because it looks nice. He even goes on dates and through the motions of romance because he thinks he should.

We’re told in flashbacks how his foster father rescued him from the most horrific circumstances and how he recognized Dexter’s dark side at an early age. But rather than “cure” him, he encouraged Dexter to cultivate his grim gifts and use them to cleanse society of killers and predators beyond the law’s reach.

Dexter’s role as a serial killer vigilante may make him palatable to some, but the show’s gruesomely clinical depiction of dismembered bodies and of Dexter’s tidy procedures takes it beyond even the casual morbidity of the “CSI” franchise.

That said, Dexter’s macabre humor and icy self-awareness make him both a compelling character and the perfect narrator for a tale that gets stranger and creepier as it unfolds.

¢ Speaking of raising the dead, get ready for a revival of “Knight Rider” (8 p.m. Sunday, NBC), a special one-night salute to the campy fantasy series (1982-86) in which star David Hasselhoff was upstaged and (some think) out-acted by his automotive co-star, KITT (Knight Industries Three Thousand).

Look for Hasselhoff in a special guest appearance in this odd February sweeps special that was not made available for review.

Just when you think they learned from the tepid reaction to “Bionic Woman.”

Today’s highlights

¢ “True Hollywood Story” (5 p.m., E!) profiles the Beckhams.

¢ Dr. Sanjay Gupta looks at the role of the presidential doctor on “First Patient” (7 p.m., CNN, today and Sunday).

¢ A dry cleaner’s error may hold clues to a murder on “Law & Order” (9 p.m., NBC).

Sunday’s highlights

¢ The Daytona 500 celebrates its 50th birthday (1 p.m., Fox).

¢ Scheduled on “60 Minutes” (6 p.m., CBS): a controversial heart medicine; Gustavo Dudamel, the 26-year-old musical director of the Los Angeles Philharmonic.

¢ Arctic bears face an uncertain future on “Nature” (7 p.m., PBS, check local listings). F. Murray Abraham narrates.

¢ Templeton receives unwanted attention on “The Wire” (8 p.m., HBO).