Marsha Norman takes an alternately playful and somber trip through the mind of an ailing writer in Trudy Blue, a whimsical comedy-drama that will face unflattering comparisons to the Pulitzer Prize-winning Wit, which also premiered in Gotham at the MCC Theater, and treated in similar style the story of a literary femme facing cancer. Although Trudy Blue is not of Wit's caliber (come to think of it, Wit isn't quite all it's cracked up to be, either), Norman's play riffs on an intriguing idea and has its poignant moments. It also boasts an almost embarrassingly accomplished cast. But it doesn't live up to the promise of its inventive concept, only catching dramatic fire in the final minutes.

The play is unfocused by definition: It takes place inside the head of the novelist Ginger (Polly Draper) as her mind replays or anticipates a series of incidents whose reality the audience can only glancingly gauge. Conversations and actions recur in contradictory ways, keeping the line between Ginger's nonstop fantasizing and the real world firmly blurred. It's an appealing premise. Who has not, on occasion, paused to wonder at the fabulous series of replayed conversations, dreamed encounters and surreal fears that circulate constantly through the active imagination?

In the opening moments, it seems Ginger has been given a tremendous reprieve: A possible lung cancer diagnosis has been downgraded to pneumonia. But her relief is short-lived. As she complains to her alter ego, the play's title character (Sarah Knowlton) and the protagonist of her novels, the brush with death has inspired Ginger to examine her dissatisfactions, which include a somewhat generically unhappy marriage and a snippy relationship with her teenage daughter.

Ginger's meandering journey through the byways of memory and imagination takes some broad comic turns in Michael Sexton's production. Not all of them are particularly rewarding. Much of the interplay between Ginger and Trudy, who talks back to her creator even as she is made to enact a chapter from a rather trite romance novel, is coy and preposterous. Particularly embarrassing is a scene in which Trudy arrives in tart attire to show Ginger how to turn on the musician she's idly thinking of having an affair with. Knowlton has trouble bringing dignity to this fuzzy conceit.

When it's revealed that Ginger is, in fact, dying of cancer, the play gains emotional texture as Draper's wry performance turns gravely tender. As Ginger awaits the final verdict, watching in agony as a doctor examines an X-ray, she speaks her reeling mind's frenzied thoughts with an onrushing sense of vertigo that's touching and terrifying. Here the play's premise finally bears vivid dramatic results, and they carry through to the play's end, as Ginger makes peace (or imagines it) with her husband and daughter, banishing the harrying Trudy to connect more deeply with the people in her life, rather than the phantom doubles she's more comfortable confronting.

But these resonant final minutes are preceded by an hour of wheel-spinning replays that simply aren't written with enough wit or revealing insight to justify the wait. Some talented actors are left with precious little to do: John Dossett is better as Ginger's tetchy spouse than as her would-be lover; Julia Mellvaine brings authentic angst to her portrait of a teenager in minor turmoil; Aasif Mandvi (of Sakina's Restaurant) is capable in a trio of small roles. Most surprising is the presence of The Life's terrific Pamela Isaacs in the negligible role of Ginger's agent Sue.

Mark Wendland's nifty set may also remind audiences of Wit, since its sliding screens are manipulated by the performers much in the manner of the hospital room curtains in that other play. It's a more artful piece of design, however, in the service of a lesser work.

For the record, both plays premiered in 1995, Wit at South Coast Repertory in Costa Mesa, Calif, and Trudy Blue at the Humana Festival in Louisville, Ky.