“Nova” (7 p.m., PBS, check local listings) presents “The Spy Factory,” an expose of the National Security Administration (NSA). Three times the size of the CIA and many times more secretive, the NSA’s own initials have inspired many nervous jokes, such as “No Such Agency” and “Never Say Anything.”

“The Spy Factory” looks at two major concerns about the agency. Many worry about its potential to eavesdrop on ordinary Americans’ phone calls, cell phones and Internet activities. But the principal concern addressed in “Spy Factory” is the fact that the agency may be too secretive to be of practical use.

The documentary spells out a detailed indictment of the NSA, arguing that it was spying on Al Qaeda and Osama Bin Laden from 1996 forward and that it had specific intelligence about men who would become 9/11 hijackers, but it refused to share that information with either the CIA or the FBI.

The NSA is so secretive that it was not examined in depth by the 9/11 Commission.

In a remarkable historical coincidence, several of the 9/11 hijackers who later crashed into the Pentagon would check into a motel room in Laurel, Md., an anonymous spot within sight of NSA headquarters.

“Factory” asks serious questions about the wisdom of trusting the NSA — the institution that seems to have botched its role prior to 9/11 — with the vast program of warrantless wiretapping of American citizens.

• “Frontline” (8 p.m., PBS, check local listings) correspondent Dave Iverson produced “My Father, My Brother and Me,” a look at Parkinson’s disease, which has taken a heavy toll on his family.

He talks to researchers who have come up with an experimental brain surgery that may be a breakthrough treatment. He also interviews actor Michael J. Fox and journalist Michael Kinsley, both afflicted with Parkinson’s.

Talk of treatment in-evitably leads to the Bush administration’s restrictions on stem-cell research and its impact on a treatment or cure.

Kinsley observes, “Six years have gone by (since Bush’s restrictions), and those were pretty important years for people like me.” Columnist Charles Kraut-hammer, who suffers from a spinal-cord injury that might be helped by stem-cell research, remains of two minds. While he supports research, he understands Bush’s motives and his desire to draw a moral line in the sand and to treat stem cells that have the potential to become human life with the utmost respect.

Tonight’s other highlights

• The Hollywood phase begins on “American Idol” (7 p.m., Fox).

• A mystery virus looms on “Fringe” (8 p.m., Fox).

• Olive-oil pressing and diaper duty on “Dirty Jobs” (8 p.m., Discovery).

• Two female victims vanish in plain sight on “Without a Trace” (9 p.m., CBS).

• “Independent Lens” (9 p.m., PBS, check local listings) presents “Adjust Your Color,” a profile of Petey Greene, a radio talk-show host from 1977 to 1983 with a large audience in Washington, D.C. Don Cheadle, who portrayed Greene in the feature film “Talk to Me,” narrates.

• Tiny bikes and lumberjacks abound on “Wreckreation Nation” (9 p.m., Discovery).

• The British white-collar comedy “The IT Crowd” (10 p.m., IFC) enters its second season.