Detective novelist Jessica Fletcher returns in the TV movie “Murder She Wrote: The Celtic Riddle” (8 p.m., CBS). Angela Lansbury’s well-known character travels to Ireland when she’s named in the will of Eamon Byrne (Peter Donat), a man she met decades earlier. Eamon’s last testament is a muddled affair. For, in addition to money and property, he has left his heirs clues to a treasure hunt. But, he insists, they’ll only find the prize if they cooperate with each other.

But that won’t be easy. The clues are a confusing jumble of cryptic, Celtic aphorisms and Gaelic verse. And Byrne’s family is the crankiest band of Irish stereotypes to hit the screen since the wee green monster chased Jennifer Aniston to his pot of gold in the 1993 horror movie “Leprechaun.”

Soon, the Byrne brood begins to quarrel, fight and die under mysterious circumstances. And, even worse, we have to endure “Riverdance”-type performances! Only diehard “Murder” fans should sit still for this weak serving of blarney stew.

l Unlike most documentaries that emphasize the fabulous side of the fashion racket, “Models: The Real Skinny” (8 p.m., A&E) explores the often brutal aspects of the beauty business.

Tonight’s other highlights

• Scheduled on “Dateline” (7 p.m., NBC): the serial arsonist who terrorized Phoenix.
• Keanu Reeves and Laurence Fishburne star in the 1999 head-scratcher “The Matrix” (7 p.m., Fox).
• A wealthy wine heiress (Cynthia Gibb) investigates a murder in the 2003 mystery “Mary Higgins Clark’s ‘Crime of Passion”‘ (7 p.m., Pax).
• Kyra mulls a big move on the second-season finale of “Reba” (8 p.m., WB).
• Scheduled on “NOW with Bill Moyers” (8 p.m., PBS): software tycoon Bill Gates discusses his life as a philanthropist and his decision to donate billions of dollars to charities addressing public health issues.
• Missing runaways may be linked to a clone quack on “Law & Order: Special Victims Unit” (9 p.m., NBC).
• Scheduled on “20/20” (9 p.m., ABC): Mother’s Day interviews with Queen Latifah and Marg Helgenberger and their mothers.
• Scheduled on “On the Record with Bob Costas” (10:30 p.m., HBO): Michael Douglas, Michael Moore and Denis Leary.