The new head-scratcher “The Night Listener” spins a yarn about a radio-show host who suspects a mysterious teenaged writer of not being who he claims. Entering a culture that’s recently seen (and seen through) the likes of J.T. Leroy, it arrives late, soggy, and starring Robin Williams. Before its quick getaway, the barely feature-length movie pimps a couple of big ideas about the lies people (and writers) tell themselves and others. But thudding dramatic inertia and a nagging air of pointlessness aggravate the novelty of the premise.

Of course, the Leroy affair was technically the also-ran among frauds. Armistead Maupin’s 2000 novel, the basis of “The Night Listener,” fictionalizes and reworks the author’s actual friendship in the 1990’s with a 14-year-old boy who claimed to be stricken with AIDS and had written a moving autobiography. The boy turned out to be the creation of the woman posing as his mother, who, in turned out, had successfully duped Mr. Maupin and celebrities from Oprah Winfrey to Keith Olbermann, Mr. Rogers, and, for shame, Jermaine Jackson.

Mr. Maupin has adapted his book into a facile screenplay, still centered on his surrogate character with the radio-ready name of Gabriel Noone. Gabriel (Mr. Williams) is a reflective late-night storyteller of the sort thousands love (and thousands others, let’s be honest, find insufferable). He mines his life for broadcast material, but when his longtime boyfriend moves out, it’s too much to bring to the mic.

Gabriel is well ensconced in gloom and self-pity when an editor friend hands him a must-read manuscript by a sick teenager named Pete (Rory Culkin). The author’s plight moves him, and seemingly within days the two are phone buddies and calling each other “dude.” The suddenness of their bond is one of the movie’s many miscues — suspicious enough to suggest a thriller before it’s sustainable, and too hollow to emotionally ground what follows.

At some point — a point several steps behind the audience — Gabriel starts to believe the doubts of his mostly-ex-boyfriend (Bobby Cannavale) and bookkeeper (an incongruously ironic Sandra Oh). He flies out to Wisconsin, where the boy and his mother Donna (Toni Collette) are supposed to live. A poorly paced series of shell games follow that quickly degenerate into unrecoverable B-thriller nuttiness and a lot of freakiness on Ms. Collette’s part.

Throughout, Mr. Williams underplays by his standards, but the role encapsulates his tragic career as a serious actor. Of late, Mr. Williams has taken one mawkish part after another (“House of D,”anyone?). In each case, “The Night Listener” included, he bows pretentiously beneath the weight of sentiment, as if to say, “Look how sad this is. And I’m doing it all for you.” Gabriel is therefore the perfect fit: a desperate character forever chasing a sentiment, an idea, that rings false to others.

Ms. Collette, too long the best-kept secret in Hollywood, throws herself with typical and lovely gusto into her underwritten character. Donna, who is also blind, is a kind of inversion of Norman Bates, and Ms. Collette sets herself into a taut, disturbing surface of twitchy vulnerability and wounded cunning.But although Donna is clearly the most interesting person in the saga, the movie mainly sees fit to ship her on the fast boat to Cuckooland, a ridiculous bundle of betrayal and floppy-hatted menace. Director Patrick Stettner basically repeats the too-far-too-fast veers of his last feature, “The Business of Strangers,” (itself an inversion of another source, “In the Company of Men”).

“The Night Listener” has a worked-over feel, whether from rejiggering or mere aging since its purchase at Sundance. Yanked through mismatched tones and threaded through a number of plot holes, the movie ultimately fails less because of its premise than its corny, faux-elegant message about the self-deceptions and selfishness of fiction and love. Messrs. Stettner and Maupin expect the same suspension of disbelief as their star sucker, but it’s too much to ask, especially if you’re not a gullible celebrity with time to kill.