"This bond between a lonely child and a grandmother is serious love," announces the straightforward poetess Diana (Julia Brothers) in the opening moments of Sandra Deer's unsteady, Alzheimer-themed Tonight the Subject Is Love, given its West Coast premiere at Mill Valley's Marin Theatre Company. The "lonely child" is Diana's now-grown biology professor son, Josh (Anthony Veneziale), and the grandmother is Ruby (Wanda McCaddon), an emotionally demanding firecracker of a woman whose gradual mental deterioration forms the otherwise weak structure of Tonight.

It is a sign of the playwright's overall failure and the work's clunky plotting that after Diana makes the statement about the "serious love" between grandma and grandkid--teasing us with hints of powerful intergenerational drama to come--the story then meanders into other waters, never giving us, in the few scenes that ensue between Josh and Ruby, any real sense that their love and bond was ever that extraordinary.

It is just one of many moments in the play when the playwright promises upcoming emotional payoffs that never actually come. This is not to say that Deer's well-intentioned play, an examination of one small family dealing with the gradual disintegration of their complicated matriarch, is without emotional power. There are lovely moments, some of them quite powerfully acted, especially true in the second-act performances of McCaddon and Brothers.

Director Jasson Minadakis--MTC's new artistic director, making his directorial debut with Tonight, also the first play he hand-selected to the company--does a competent enough job in staging the choppy proceedings, with an eye toward simple visual pleasures. You could take a snapshot of the show at any moment and the onstage composition would make a pleasing picture. Minadakis comes to MTC with a reputation for energetic leadership and a taste for groundbreaking writing. Disappointingly, his freshman effort in Marin gives him little opportunity to show what he might be capable of with a truly meaty play.

Alzheimer's is an increasing reality in America; the facts and figures of this are doled out in "be afraid, be very afraid" detail throughout the play (at one point a character actually addresses the audience to say, "This could happen to you"). There is a great script to be written about the specific sadness that comes from watching a powerful mind dissolve, but disappointingly, this is not that play.

Tonight the Subject Is Love runs through June 10 at the Marin Theatre Company. Tuesday and Thursday-Saturday at 8pm; Wednesday at 7:30pm; Sunday at 2pm and 7pm. Also May 23 and 31, guest lecture at noon, performance at 1pm; June 9 at 2pm. May 30, director Q&A following performance. $19-$47; Tuesday, pay what you can. 397 Miller Ave., Mill Valley. 415.388.5208.

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