No one can call Christopher Shinn a chicken. The playwright tried to address post-September 11 existence in “Where Do We Live,” and though he met with mixed results, he got points for his directness and clarity of attack. Now in “On the Mountain” at Playwrights Horizons, he again aims straight at a public tragedy – the aftermath of Kurt Cobain’s death – in order to tell a story about incurable loneliness. It’s another incomplete effort, with relationships thinned too far to have much effect. But at least Mr. Shinn chooses to write about addiction and depression, realities that our theater usually avoids.

Mr. Shinn also may be the first playwright to have the iPod as a plot device. We first see the shiny, white icon around the neck of Jaime (Alison Pill), a teenager drinking Coca-Cola, listening to Radiohead, and writing stories for her group therapy sessions. Her mother Sarah (Amy Ryan) arrives home with something else around her neck – the affectionate man-boy Carrick (Ebon Moss-Bachrach) who followed her home from her waitressing job. Carrick and Sarah soon embark on a romance, despite her desperation, Jaime’s careering self-esteem, and Carrick’s ulterior motives.

Sarah’s past, one she has put behind her for sobriety’s sake, lends her incredible glamour in Carrick’s eyes. The one-time girlfriend of a junkie rock star (the names are changed, but clearly Cobain is his inspiration), Sarah is a tangible, living link to a mythic creature. She may also have his “lost recording,” and the search for it leads Carrick to her door.

Once inside, however, he finds his motives changing. Jaime touches him deeply, and Sarah’s fight with alcoholism makes her leery of discussing her party-girl past. While all of them try to tiptoe around their wounds, they exhume themes of exclusion and art’s ability to assuage loneliness.

Director Jo Bonney (aided by Neil Patel’s set design and the costumes of Mimi O’Donnell) goes for a quotable realism. Sarah’s kitchen is complete, down to the set of spare keys by the door, and Jaime’s sloppy ponytail and flip-flops look like she wore them in off the street. She also lavishes attention on the individuals: Ms. Bonney and company flesh out a self-consciously unpoetic script with intricate character embellishments.

The neatest construction springs up between Jaime and the willowy Carrick. Though the script doesn’t much allow for it, the actors thrum with nervousness and unconscious sexual energy. It’s a vital third side to the triangle, and they seem to do it all with nearly nothing.

Ms. Ryan, the recovering addict who may be substituting sex for booze, stands outside their youthful highs and lows, choosing self-preservation over Weltschmerz. A choice for numbness is a hard one for an actress, and Ms. Ryan comes out of the evening with fewer memorable moments than Ms. Pill or Mr. Moss-Bachrach. Each character takes his turn at feeling the outsider, but Sarah’s exclusion is one she has to choose again and again.

Mr. Shinn’s play doesn’t particularly exceed its own parameters – though it talks about addiction and loneliness, there is no transparent, universal sensation to be had. When his words fail to kindle anything between Carrick and Sarah, the play’s most important shot at emotional accessibility misses. If there were any heat, any palpable need between the two adults, their tearing apart might have brought the show together.

Instead, the show blends intriguing ingredients in a cold pot. It’s like the giant bowl of cereal Jaime writes about in a short story: It seemed like a good idea to mix the sugar bombs and the wheat squares, but sometimes it’s best to tip a saccharine mess down the sink.

Until March 13 (416 W. 42nd Street, between Ninth and Tenth Avenues, 212-279-4200).