1) “Sullivan’s Crossing,” 8 p.m., CW. This drama is sometimes as gentle and peaceful as its Nova Scotia setting. Last week, however, ended with a jolt: Two college guys were with a teen girl, when one accidentally shot Frank; they grabbed the girl and ran. That story wraps up now, leaving more room for the main plot, which is fairly good: A big-city surgeon, facing legal troubles, has retreated to the campgrounds where her father and Cal (Chad Michael Murray) and others cling to secrets.
2) “Magnum P.I.,” 9 p.m., NBC. There’s so much here – fast cars, blue skies, likable people – that we’ll almost forgive a weak story. Finding bodies at a two-car crash site, authorities assume the lone survivor was a driver and at fault. Guilty unless proven innocent, he faces years in prison. It’s a poor plot, but it’s surrounded by other stories (including TC’s recovery) that keep us watching.
3) “Quantum Leap,” 8 p.m., NBC. Let’s credit this show for spot-on typecasting: Tim Matheson plays someone who calls himself “a former TV star who’s best days are behind him.” That’s in the first minute; then the show sags. A flaw in the “leap” program caused Ben to disappear for three years; his fiancee (and holographic advisor) began a new romance. Merging that story with the current leap, this oft-excellent series emerges with a so-so episode.
4) “The Challenge: Battle For a New Champion” opener, 8 p.m., MTV. Six days after the finale of CBS’ spin-off (“The Challenge: USA”) ended, the original returns. It’s the 39th edition, in 25 years, for a show first called “Road Rules: All Stars.” This time, the 24 contestants have all been on previous editions, without winning. They get a new shot, but previous winners sometimes try to block them.
5) “Nature” and “Nova,” 8 and 9 p.m., PBS. Both shows offer ambitious mini-series. For “Nature,” it’s the start of a four-parter that creates animatronic sea creatures, armed with cameras, to record the lives of the real creatures. For “Nova,” it’s the fourth chapter of the superb, five-part “Ancient Earth.” This hour starts 252 million years ago, with volcanic explosions that destroy 90 percent of life.