"Sacred Sites" (8 p.m., Smithsonian) enters a second season scouring the world for locations associated with ancient rites, rituals, belief systems and superstitions. The season begins with a trip to sites linked to legends surrounding Britain's King Arthur. The show includes interviews with experts who sort out arguments as to the reality of the fabled ruler and his Round Table.
As with many such controversies, the search for evidence seems almost beside the point. Arthurian legend has propelled storytelling in popular culture from epic poetry to "Star Wars" and "The Lord of the Rings: The Fellowship of the Ring" (9 p.m., Starz Encore).
Future episodes will explore ancient Mayan sites (Aug. 20); Spain's Camino pilgrimage (Aug. 27); legends linked to Malta (Sept. 3); Egypt's cult of priestesses (Sept. 10); and Teutonic tales associated with the Nazis (Sept. 17).
-- Speaking of special spots, "Evil Lives Here" (9 p.m., ID, TV-14) enters its fourth season. This paranoid true-crime re-enactment series features friends or loved ones who slowly discover that the person they've welcomed into their lives is actually a homicidal maniac. Tonight's season opener follows the devout follower of a cult leader who comes to realize he might not be on the side of the angels.
-- Now streaming on Acorn, the British police procedural drama "Five Days: The Train" follows characters from a diverse community in the period after a newborn is found abandoned in a hospital bathroom, and a young immigrant commits suicide by jumping in front of a train. Suranne Jones ("Vanity Fair") and David Morrissey ("The Walking Dead") star.
-- As part of its Summer Under the Stars festival, TCM dedicates the day to the films of George Brent. Hardly a household word today, he was a frequent co-star to Bette Davis and plays her doctor in the 1939 melodrama "Dark Victory" (8 p.m., TCM). Arguably the best movie to ever feature Ronald Reagan.
He also appears with Barbara Stanwyck in the business satire "Baby Face" (9 a.m., TCM). Its implicit and explicit theme that a woman could sleep her way to the top of the corporate ladder outraged puritans and helped usher in the era of the Hollywood Code, which regulated sexuality and taboo topics on screen well into the 1960s.
-- "Frontline" (9 p.m., PBS, check local listings) presents the two-night special "Our Man in Tehran," following journalist Thomas Erdbrink as he encounters friends and his wife's relatives going about their everyday lives in the Islamic Republic of Iran.
Tonight's other highlights
-- Philadelphia finals unfold on "American Ninja Warrior" (8 p.m., NBC, TV-PG).
-- The top 10 face elimination on "So You Think You Can Dance" (8 p.m., Fox, TV-PG).
-- Liam receives help from an unlikely character on "Salvation" (9 p.m., CBS, TV-14).
-- Jimmy needs a job on "Better Call Saul" (9 p.m., AMC, TV-14).
-- An engineer's work may have cost him his life on "Elementary" (10 p.m., CBS, TV-14).
-- Ten men perform for a brokenhearted woman on "The Proposal" (10 p.m., ABC).
-- As Dud discovers the lodge's lore, Ernie sets his sights on leadership on "Lodge 49" (10:05 p.m., AMC, TV-14).
Confrontations arise on "Bachelor in Paradise" (8 p.m., ABC, TV-14) ... Adam's estranged brother proves surprising on "Mom" (8 p.m., CBS, r, TV-14) ... Illusionists audition on "Penn & Teller: Fool Us" (8 p.m., CW, TV-PG) ... A conversation becomes animated on "Life in Pieces" (8:30 p.m., CBS, r, TV-PG).
On two helpings of "Whose Line Is It Anyway?" (CW, TV-14), Carmen Electra (9 p.m.) Greg Proops (9:30 p.m., r) ... "Dateline" (10 p.m., NBC).
Spike Lee sits down on "The Daily Show With Trevor Noah" (11 p.m., Comedy Central) ... "Conan" (11 p.m., TBS, r) visits Mexico ... Jimmy Fallon welcomes Carmelo Anthony, Chris O'Dowd and August Greene on "The Tonight Show" (11:35 p.m., NBC) ... Glenn Close, Topher Grace and Low Cut Connie visit "Late Night With Seth Meyers" (12:35 a.m., NBC) ... Rob Reiner, Emily Mortimer and John David Washington appear on "The Late Late Show With James Corden" (12:35 a.m., CBS).