Pity the detective story. It used to be about evidence and observation, logic and reason, deduction and, yes, “detection.” Now the storied realm of Holmes and Spade and Marlowe has been reduced to a corridor to the supernatural.

“Past Life” (8 p.m., Fox) takes this trend to the ridiculous and beyond, opening a mysterious antechamber linking the unbelievable with the uninteresting.

Kelli Giddish stars as Dr. Kate McGinn, an expert in “past life” regression, haunting visions and episodes that are nature’s way of telling us we’ve been reincarnated and that our former selves still have stories to tell. And evidence to reveal. She’s aided in her sleuthing by Price Whatley (Nicholas Bishop), a troubled former cop who plays gruff skeptic to her bewitching witch doctor.

Over the course of the first episode, we meet a troubled teen whose basketball practice is frequently ruined by delirious spells. During these unpleasant reveries, he witnesses scenes of a buried past. Not to give too much away here, but he may or may not have been a little girl in a prior existence, and his spirit may be the only witness to his or her own murder.

• “American Idol” (7 p.m., Fox) enters its Hollywood-week boot-camp phase, winnowing a list of 180 yellow-ticket winners to 12 contestants of each gender. It’s also the debut of the new permanent judge, Ellen DeGeneres.

• The anticipation for the sixth season of “Lost” (8 p.m., ABC) was so fevered that many are already complaining that last week’s two-hour debut was not up to snuff. I disagree. Aware that its audience was hungry for answers, “Lost” offered more questions, as well as two new stories, the siege of what I like to call the Kung Fu castle and the diaspora of the Flight 815 passengers into a parallel Los Angeles.

Tonight’s other highlights

• An annotated recap of last week’s “Lost” (7 p.m., ABC) helps viewers catch up.

• “Extreme Cave Diving” on “Nova” (7 p.m., PBS, check local listings) looks at a dangerous corner of science that examines a world from before the last ice age.

• “Flying Cheap” on “Frontline” (8 p.m., PBS, check local listings) looks at the rapid rise of unsafe and deregulated regional airlines.

• Scheduled on “Real Sports with Bryant Gumbel” (8 p.m., HBO): Johnny Weir.