Sometimes the magic is there, everything works. The play is unexpectedly great, the star has a towering moment, the director bats a thousand with imaginative staging. We don’t get to feel this all the time, so let me blabber for a minute here about Mary Louise Parker in “The Sound Inside,” written by Adam Rapp and directed by David Cromer. There’s also a newcomer in this two-hander, Will Hochman, who suddenly has a theater career at the age of 22.

No one could really tell what was going on with extra long preview time over at Studio 54. Jeffrey Richards and Lincoln Center were renting the theater from the Roundabout to put on “The Sound Inside,” a new play really no one knew anything about. Just the idea of new play these days is like a gift from the heavens. Basically, we’re awash in revivals and non-revivals like “To Kill a Mockingbird.” I mean, “Who’s Afraid of Virginia Woolf?” is coming back again. And again.

But here’s Adam Rapp, with a resume of excellent off Broadway plays, making his debut. Here’s Mary Louise Parker, so good in “Proof” almost 20 years ago, known better for her TV work in “Weeds” and some Broadway shows that garnered good notices for her but just didn’t make it. And then you have David Cromer, acting in and directing 5 hits in a row over the last decade including the Tony winner, “The Band’s Visit.”

Who can say which ingredient was the winner? Mixed together, all the elements of “The Sound Inside” make for an evening in the theater we started to think wouldn’t happen again. Rapp told me his play draws on autobiographical material– his mother died of cancer in 1997. And so Parker’s Bella, a college professor without family but smart and funny, receives her diagnosis. And then she meets a new student, Christopher, also a loner, maybe troubled, but he has a spark. Bella and Christopher’s connection is not what you think it is. Rapp steers clear of every cliche. Their 90 minute saga, without intermission, just keeps taking unexpected and welcome turns.

Hochman reminded me of Jesse Eisenberg when he was starting out, or Alex Sharp (of “Curious Incident” fame). Super articulate and sensitive, he’s not naive, so he’s a good conversational match for Bella, who’s at a crossroads. I’m glad Christopher is there in person. But really Bella could just do the whole thing as a monologue. Parker just has her right in her palm. She’s in the zone, as they say. She gives a stunning spot on performance that will be remembered for a long time to come.

And here’s the real plot twist: this is a limited run. The Roundabout has to go back to its schedule. Parker has already signed on to star in another play this spring. She’ll co-star with David Morse in a revival of “How I Learned to Drive.” Everyone should have this dilemma! I hope she can come back in another run of “Sound Inside” after that. And she’ll have to decide which show to take to the Tony Awards. This one must absolutely be the one.

Note to Tony voters: much as with “Waverly Gallery,” and Elaine May, get in to see this before it closes.

In the audience tonight, lots of cool people including Susan Sarandon, Molly Ringwald, Counting Crows’ Adam Duritz (a former Parker boyfriend), plus BFF Kathy Najimy (who was kvelling), and “Rent” star Anthony Rapp, whose brother is the playwright. Plus Parker and Billy Crudup’s tall, good looking 15 year old son who told me he’s going to get into directing as well as acting. He’s got the genes!

I am flummoxed by the new revival of Tennessee Williams’ “The Rose Tattoo,” which opens this week with Marisa Tomei as the sexy, confused Italian widow Serafina. Tomei, who has a long theater resume, knows what she’s doing. But she’s the only one. Rarely have I seen a star go one way and the production go the other way in a piece that is well known to everyone at least in theater.

You hear the name Tennessee Williams and you don’t think “slapstick.” There’s humor in “The Rose Tattoo,” and Serafina can be daffy and sassy, but Lucy Ricardo? No. Director Trip Cullman, who did fine work reviving “Six Degrees of Separation” and “Lobby Hero,” has just misunderstood this play completely.

Serafina is a Sicilian transplanted to the Gulf Coast of Louisiana in 1951. She sings the praises of her husband, a truck driver, as a great lover and partner. But he dies, and she learns he’s been having an affair. (It’s unclear in this version how long this takes– a few days or years.) She’s left with a 15 year old daughter who wants to lose her virginity. That’s Act I. In Act 11, a hunky younger truck driver wanders into Serafina’s seamstress business, and they fall for each other.

None of this is particularly funny, but someone has told the actors to “sell it.” The whole tone is off, and it’s almost impossible to follow what’s going on in the first act. Tomei is working, working, working. She is gorgeous and smart. But it’s like herding cats. She can’t get the cast on the same page, and neither can Cullman. Working against them is an extremely odd set. It’s inside, outside, who knows? In the distance on video is supposed to be the Gulf, but this Gulf has waves like it’s Ditch Plains beach in Montauk. A surfer could float in at any minute. Plus there are children running around constantly. Is there a daycare center nearby?

More even than George Costanza, I am such a fan of Marisa Tomei. See this production just to see her. But don’t hope to learn anything much about Tennessee Williams. This streetcar has too much graffiti.