It’s 1942, and Simon gives us a nuclear family that clearly has some protons missing. Grandma Kurnitz (Irene Worth) is a fearsome German-Jewish tyrant who’s terrorized her children, now grown: Bella (Mercedes Ruehl) is a good-hearted soul who’s not right in the head. Gert (Lauren Klein) is so nervous that she sometimes forgets to stop talking when she inhales, so that her speech is punctuated by death rattles of fear. Eddie (Mark Blum) is panic stricken when he has to persuade Grandma to take in his young sons Jay (Jamie Marsh) and Arty (Danny Gerard) so that he can go off to a defense job. Only his brother Louie (Kevin Spacey), a small-time gangster, seems unafraid of Grandma. Or is he?

Starting out bonkers in Yonkers, the family gradually deepens and darkens. These are all wounded human beings. Grandma, seemingly a monster of negativity - unloving, unfeeling, uncaring - turns out to be the most deeply wounded of all. Simon even dares to associate her with the Holocaust, and succeeds. The showdown scenes between Bella and her mother are the strongest he’s ever written.

Simon finds the right tones and rhythms for three generations, and they’re nailed down by his longtime director Gene Saks and an extraordinary ensemble. Worth and Ruehl dig deep and fly high. With her cane thumping as her voice fires rebuffs and reprimands, Worth embodies the casualties who’ve had the love battered out of them. Ruehl is piercingly funny and achingly tragic as Bella, who has a child’s mind in a woman’s body. This is American acting at its best.

Was there a Bella in Neil Simon’s life? Only inside Simon himself. Cheerfully he admits: “When Bella tells how the kids in school would yell at her, ‘Hey Bella, the Lost and Found called. Come and get your brain,’ well, I’ve gone through periods like that, when I was totally disoriented. During the writing I went through the same pain that Bella does.” One period of disorientation was the death of his first wife, Joan, from cancer at 39. “What that leaves you with is enormous guilt,” he says. This led to extensive psychoanalysis. “It never cured me of anything,” says Simon. “But it made me aware. Since I don’t have a formal education, that was my education.”

But Simon’s informal education was even more important for his insight into a character like Grandma, who exerts such ruthless emotional control over her children. “My mother used to tie me into my high chair so I wouldn’t fall out,” he says. Many years later that feeling of constriction and control has led to a play in which a mother controls her daughter so that she won’t “fall out” into a world where she can be hurt by her emotional vulnerability.

In “Lost in Yonkers” Simon seems at 63 to confront his own vulnerabilities without skipping behind a screen of gags. He is divorced but friendly with his second wife, actress Marsha Mason, and he recently remarried his divorced third wife, Diane. “I’ve always learned more from the women in my life,” he says. “The fact that I’m not in analysis now means that I’m not emotionally troubled at all.”

Perhaps it’s this sense of release that allows Simon, the legendary nice guy of the American theater, to insist that he’s not really that nice. “One of my friends said, ‘Neil is one of the nicest persons I’ve ever met and I hate him.’ I told him I was really a shit underneath. There’s a Jekyll and Hyde side to me. I’ve experimented with becoming irresponsible, morally and every other way. I wanted to see what’s on the other side.” Aha, let’s hear about these experiments. “Don’t ask for details,” says Simon. They may well show up in his future work. He says he wants to write about the period in his life when he was ill, confused, “too petrified to cross the street.” Maybe Simon is creating a new kind of comedy for our time of dislocation.