In Sarah Ruhl’s new play, “How to Transcend a Happy Marriage,” two middle-aged married couples, long-time friends, find themselves fascinated with a young woman nicknamed Pip ( Lena Hall, Tony winner for Hedwig and the Angry Inch) who lives and loves with two men, in what they call a polyamorous relationship, or a throuple, or a triad. The two couples decide to invite the throuple to a New Year’s Eve party.

“And our lives would change forever,” George (short for Georgia), portrayed by Marisa Tomei, says to the theatergoers sitting politely at Lincoln Center’s Mitzi Newhouse Theater.

It’s not actually clear that their lives do change forever. But ours certainly don’t.

The New Year’s Eve party ends in an orgy, right before intermission. In Act II, Ruhl’s play takes a series of surreal turns, in an apparent but by no means straightforward attempt to tell us something about love and marriage; and the spirit and the flesh; and the conflict between our animal desires and our human duties, as well as our efforts to reconcile these two natures.

Ruhl is a lovely writer, capable of witty aphorisms, sophisticated dialogue, humorous set-ups, and a theatrical sense of wonder. She also has a tendency towards the twee. All this is on display in “How To Transcend a Happy Marriage,” but this play doesn’t come together as effectively as some of her previous theater that touches on similar territory. She has written about love and marriage in my favorite of her plays, “Stage Kiss “; about spiritual matters, in “The Oldest Boy” ; and, in her only play on Broadway so far, “In The Next Room, or the Vibrator Play,” she has written satirically about the conflict between our animal desires and our bourgeois habits.

The strength of “Happy Marriage” is in the characterization of Lena Hall’s Pip, who isn’t just polyamorous. She is a free spirit who slaughters animals when she wants to eat meat, seeing it as the only ethical way to be a meat-eater. She is also taking pole dancing classes. And she is something of a shape-shifter. Hall, best-known for her rock personas, seems the exact right performer for the role.

One problem is that, as reliable and appealing as the rest of the cast is, they are portraying characters that seem deliberately…bland. This even includes Pip’s boyfriends, a mathematician named David (Austin Smith), who talks about Pythagoras, and Freddie (David McElwee), who doesn’t have a job: “It’s kind of a philosophy. I think, I walk. I try not to leave any imprint. Or footprint…I went to Harvard.”

Pip’s liveliness contrasts with the two couples’ banal bourgeois existence. Pip makes a living as a temp at a legal aid office; this is where she met Jane (Robin Weigert ), who works there as a litigator. Her husband Michael (Brian Hutchison) writes jingles. I don’t even remember what the other couple do for a living, except that Marissa Tomei’s George is assigned narrator duties and also gets long ruminative monologues. These sound as if they might be perceptive, but they existed in a spiritual realm somewhere above my head.

Here is what might be a typical exchange during the New Year’s Eve Party, an example of the ways in which “How to Transcend A Happy Marriage” manages to be simultaneously entertaining and tedious:

Pip: The thing about being bisexual that’s tedious is you constantly have to announce yourself. It’s like, if you decide to be a vegetarian, you don’t go around reminding people, well I’m technically an omnivore. You know?

Paul:So if you’re a monogamous bisexual, does that make you a liar all the time?

David: I sort of think so. But monogamy is a construct that will seem passé in the next century. So will race. The whole world will be like Brazil.

George: I love Brazil.

Michael: Pistachios?

Freddie: Yes, please. I love pistachios at a party. Gives you something to do with your hands. I never know what to do with my hands while I make small talk.

All this is before the fanciful twists of the second act, which I shouldn’t describe, although it wouldn’t matter much if I did. I’ll only say they take place in a forest, a jail cell, and in Michael and Jane’s home, and involve woodland creatures, and a teenage daughter, and snow, and lots of hugging.

How to Transcend a Happy Marriage
Mitzi Newhouse Theater
Written by Sarah Ruhl. Directed by Rebecca Taichman. Set design by David Zinn, costume design by Susan Hilferty, lighting design by Peter Kaczorowski, sound design by Matt Hubbs
Cast: Lena Hall as Pip, Brian Hutchison as Michael, David McElwee as Freddie, Omar Metwally as Paul, Naian Gonzalez Norvind as Jenna, Austin Smith as David, Marisa Tomei as George, Robin Weigert as Jane
Running time: two hours and 15 minutes, including an intermission
Tickets: $87
Through May 7, 2017