'THE AMERICANS': Nina (shown above) faces the threat of a FBI polygraph test at 10 p.m. on FX. (Patrick Harbron/FX)

The newly merged tribe embarks on a twisted idol hunt on “Survivor: Cagayan” (CBS at 8 p.m.), and one castaway uses ninja-like skills to sabotage another contestant.

The Top 8 perform hits from the ‘80s on tonight’s “American Idol” (Fox at 8).

SERIES PREMIERE: The gritty docu-series “Women of Homicide” (TLC at 9) takes a look at the world of homicide investigations through the eyes of three female detectives.

“Nature” (MPT and WETA at 8) presents the stories of several disabled animals that are being helped by prosthetics, from a blind golden retriever to an alligator with a rubber tail.

The “Criminal Minds” (CBS at 9) crew investigates a string of kidnappings near Memphis and searches for a commonality with each increasingly mysterious crime.

SERIES PREMIERE: Paleobiologist Neil Shubin examines the evolutionary roots of humans with evidence from DNA and fossil records on the three-part series “Your Inner Fish” (MPT and WETA at 10). In the opener, Shubin compares the evolutionary successes of fish versus humans.

Philip enlists the help of his agent Charles Duluth to get access to an early precursor of the Internet on “The Americans” (FX at 10).

The documentary “Susan Boyle: Her Secret Struggle” (Ovation at 10) explores the pains and triumps the unlikely star has faced since she skyrocketed to fame after her audition for “Britain’s Got Talent” in 2009.

“Nashville” (ABC at 10) airs a repeat from when a successful producer takes a liking to Juliette’s new song and invites her out to Los Angeles to record.

“Chicago PD” (NBC at 10) investigates a gang-related crime involving several deaths and millions of dollars in stolen cash.

Stories of online connections gone wrong are chronicled on “Cyber Stalkers” (TLC at 10), including the story of a woman who went to the internet to regain custody of her daughter.

Actress Jennifer Garner and musicians Dave Grohl and Krist Novoselic are on “The Tonight Show Starring Jimmy Fallon” (NBC at 11:35), with a performance from Stevie Nicks.

Actress Lindsay Lohan and 13-year-old nuclear scientist Jamie Edwards stop by the “Late Show With David Letterman” (CBS at 11:35), along with music from Real Estate.

Model-turned-actress Kate Upton and actor Cole Hauser come to “Jimmy Kimmel Live” (ABC at 11:35), with a musical performance from Neon Trees.

Rachel Lubitz