Joshua Harmon, the current playwright du jour of Broadway (“Bad Jews,” “Significant Other,” “Admissions”) has a new play, “Skintight” commissioned by Roundabout, playing at the Larua Pels Theatre, and staring Idina Menzel. Yes, you read that correctly: the same Tony-winning musical theater actress famous for “Take Me or Leave Me” and “Defying Gravity” is currently performing in an Off-Broadway play.

Although audiences may be initially confused — or disappointed even — to see legendary belter Idina Menzel not sing a single note in this new play, they will leave pleasantly surprised. Menzel has proven her acting chops, clearly ready to conquer the world of straight dramas just like she did musicals.

Last time the theater community saw Menzel onstage, it was for “If/Then” her forgettable musical that certainly did not become anyone’s favorite, not even for diehard Idina fans. Let’s just say If her last show had Joshua Harmon as a writer, Then it would have been much better.

Thankfully this time she has found a stellar team to work with: not only Mr. Harmon but Daniel Aukin, who directed both “Bad Jews” and “Admissions.” Mr. Aukin tackles this play with a fierce exactitude that revels in Harmon’s signature ethical ambiguities. The play concerns middle-aged Jodi (Menzel), whose ex-husband left her for a 20-something cycling instructor. To make matters worse, when she visits her fashion design father, Elliot Issac (Jack Wetherall), she discovers he is in a serious relationship with a 20-something former porn actor, Trey (Will Brittain). Also thrown into this dysfunctional tale of age, beauty, and (homo)sexuality is Jodi’s gay son, Benji (Eli Gleb).

The Elliot-Trey relationship is a thinly veiled adaptation of the infamous affair of Calvin Klein (71) and Nick Gruber (23). Gruber notoriously claimed that he isn’t gay, a sentiment echoed in the play by Trey, who says he doesn’t do labels and is “just Trey.” To further cement the parallels between Elliot Isaac and Calvin Klein, set designer Lauren Helpern constructed a minimalist chic apartment of slate grey that screams Calvin Klein.

Despite the intense arguments that ensue between the family members (and the wanna-be family member, Trey) about age disparity, youth, health, beauty, and the nature of love, the play is remarkably comedic. In particular, Menzel and Gleb act as hilarious spectators equally shocked, offended, and fascinated by the relationship between 70-year-old Elliot and 23-year-old Trey. Menzel gracefully transitions from hilarious insults, judgmental stares, and passive-aggressive suggestions, to filial concern, maternal affection, and heartfelt monologues about what it means to be in a committed relationship. The only problem with the comedy in this production is it seems as though the actors don’t realize how funny they are, and often neglect to pause and give time for the audience to laugh.

As with all Harmon plays, all of the characters are quite flawed, and audiences never know who to side with as the ethical debates get messier and messier (not to mention angrier and louder). Benji is entitled, Jodi is elitist and sex-shaming, Elliot is youth-obsessed, and Trey is greedy. Despite all their imperfections, the audience is likely to side with Jodi, not only because Menzel gives the most convincing performance, but because it is almost impossible to side with Trey or to understand what Elliot sees in him.

Trey seems to be a reincarnation of Cowboy in “Boys in the Band” or Spike in “Vanya and Sonya and Masha and Spike” — a pretty boy, but a stupid boy. However, Trey has even more stage time and more lines than either of the earlier versions of the character, and all he manages to do here is annoy the audience and come off as an idiotic sex symbol (he has an entire scene where he wears only a jockstrap) who is clearly with Elliot for the money.

Perhaps “Skintight” is less powerful, poignant, and timely than Harmon’s other recent works, but it still is a fascinating play that leaves the audiences with quite a lot to think and talk about it — most of all, the spectacular performance of Idina Menzel, who hopefully will give this acting thing a chance, sans belting.