Two superb actresses turn in terrific performances in the difficult drama “Crossed Over” (8 p.m., Sunday, CBS). After the hit-and-run death of her troubled teen-age son, Peter, writer Beverly Lowry (Diane Keaton) faces an emotional collapse. She’s seen here, still washing her son’s clothes six months after his funeral. Her life only begins to make sense after she is drawn to a photo of convicted killer Karla Faye Tucker (Jennifer Jason Leigh), because her eyes resemble Peter’s.

After a prison visit, Lowry and Tucker form an unusual bond, one that helps the former drug-addicted prostitute believe in herself for the first time in her life. Based on a true story, “Crossed Over” does not shy away from Tucker’s gruesome crime. Nor does it depict Lowry’s motives as entirely selfless. Tucker’s prison conversion to Christianity takes a back seat to her relationship with Lowry, who admits that Tucker’s faith makes her uncomfortable. After a long appeal process and protest from both religious groups and death-penalty opponents, Tucker became the first Texas female inmate since the Civil War to receive the death penalty.

The always surprising “Six Feet Under” (8 p.m., Sunday, HBO) returns for a second season. Now suffering from a brain disorder, Nate (Peter Krause) endures a session with an arrogant and unhelpful doctor and a dream-like vision of his deceased father playing Chinese checkers with two heavies from the spectral realm. Despite this David Lynch-inspired departure, “Six” falls back on its usual staple of family dysfunction, inadvertent drug use and, of course, the cadaver of the week.

Nick at Nite kicks off a five-night “Cosby Show” marathon (8 p.m., Sunday), airing four hours of the 1984-92 sitcom every night through Friday from 8 p.m. through midnight. The episodes will repeat each morning from midnight to 4 a.m., as well. Nick-at-Nite.com (www.nickatnite.com) invites viewers to vote for their favorite Huxtable offspring. The winner will be honored on Friday with an evening of repeats featuring his or her character.

Young Huxtable Malcolm-Jamal Warner (“Cosby”) joins Luke Perry (“Beverly Hills, 90210”) in the new sci-fi series “Jeremiah” (7 p.m., Sunday, Showtime) as two survivors in a world destroyed by a mysterious epidemic that 15 years earlier killed everyone over the age of puberty. Few remember their lost world as they scrape out a “Mad Max”-style existence while avoiding racist wolf packs, armed gangs and other nasties. The chatty Kurdy (Warner) and the silent, stoic Jeremiah (Perry) team up from time to time as they wander through the wasteland in search of a legendary safe place called the “Valhalla Sector.” This 20-episode weekly series is based on a graphic novel. That’s a fancy word for a long comic book.

Comic books, smelly gaming arcades and other facets of the nerd world are celebrated in the well-written cartoon special “Welcome to Eltingville” (10 p.m., Cartoon Network). Jerry, Bill, Josh and Pete, four members of The Eltingville Comic Book, Science Fiction, Horror, Fantasy and Role-Playing Club stumble through post-puberty together, much to the consternation of their screaming, unseen parents. These guys may not have a chance with girls, but they are walking encyclopedias of “Star Trek” lore, comic knowledge and sci-fi savvy.

Today’s other highlights

Jonny Moseley hosts “Saturday Night Live” (10:30 p.m., NBC).

Sean Connery and Jill St. John star in the 1971 thriller “Diamonds Are Forever” (7 p.m., ABC).

The talented Texan Renee Zellweger pleased audiences on both sides of the pond with her memorable performance in the 2001 romantic comedy “Bridget Jones’s Diary” (7 p.m., Starz). With Hugh Grant and Colin Firth.

Tommy Lee Jones stars in “U.S. Marshals” (7 p.m., NBC).

A coal-miner’s son shows a talent for ballet in “Billy Elliot” (7 p.m., Showtime).