Sarah Ruhl’s delightful backstage comedy, now in previews at Playwrights Horizons, is at heart a love letter to theater and actors. Along with loads of hilarity, there is an exploration of how permeable the border between art and life is and how hard it sometimes is to tell which is imitating which. The premise is that an actress (Jessica Hecht) making a return to the stage after a long time off for childrearing is cast in the revival of a short-lived period drams from the 30’s about a woman whose dying wish is to see her old lover again. The actor playing her long lost lover is none other than her real-life former lover (Dominic Fumusa) from whom she split acrimoniously 20 years prior. When they are forced to kiss on stage eight times a week, their affair is rekindled. For most of the play’s first hour, I was doubled over with laughter. In the opening audition from hell, Hecht demonstrates that she can be a first-class comedienne; her mannered style, which I have often found so annoying, serves her well here. The audition is followed by several funny rehearsal scenes and, finally, by opening night. Fumusa has a scene on crutches that is a comic triumph. The revelation for me was Michael Cyril Creighton, who at various points plays the butler, the understudy, the doctor and, in the second act, a pimp; he is wickedly funny in all his guises. The rest of the supporting cast (Todd Almond, Clea Alsip, Emma Galvin, Daniel Jenkins and Patrick Kerr) are fine too. At intermission, I feared that Ruhl would be unable to maintain so high a level for another act. To some extent, my fears were justified. Act Two explores the consequences of their rekindled affair and throws in another audition and a scene from another play-within-a-play. Although there are a few extremely funny scenes, the resolution is a bit anticlimactic. Neil Patel’s scenic design is excellent, as are Susan Hilferty’s costumes. She dresses Hecht in a gown that is an absolute knockout. Rebecca Taichman’s direction skillfully manages the abrupt changes of tone. I wish the second act had been as wonderful as the first, but I am grateful for the first hour, which is one of the most entertaining I have spent in a theater. Running time: 2 hours, 10 minutes including intermission.