Short can be an advantage: Shorter is better, we say. But not always, not in theater. One-act plays often suffer from insubstantiality, as if the tightness of the form prohibited tackling something significant, or from incompleteness, as in, "where's Act 2?" The result is often just an extended scene.

So the achievement of Chris Gavaler's "The Chris & Alex Show," the anchor of the first weekend of the 17th Pittsburgh New Works Festival (now ensconced at Open Stage in the Strip), is all the more unusual. It takes a quintessentially theatrical idea and explores it with great assurance and panache, and at 28 minutes it's exactly the right length, with time for several twists and turns but not enough to run out of gas.

Because of those twists, this is your spoiler alert: If you're going to this week's New Works Fest, which I recommend, and you'd like to experience it without critical interference, stop reading.

The Chris and Alex of Gavaler's title are names that can be male or female, like the "It's Pat" sketches on "Saturday Night Live." The two are significant others squabbling about their relationship. But the play starts with the Director announcing that one actor has been replaced by an understudy, who will carry a script. About halfway through, the original actor shows up and demands to play the scene, and then there's another switch of who plays whom, and another.

The surface tickler is playing Chris and Alex as male or female in every combination, the script still works. But this is no simple treatise on how love and its discontents go beyond gender. More triumphantly, "The Chris & Alex Show" is about the audience's role in making theater work.

After all, the play tells us right off these are actors: One even carries a script. Yet I found myself immediately buying into their argument. And every time the basic artifice is italicized -- when one objects that another has skipped a line, an audience member intervenes, or the actors change roles -- I immediately bought into the revised "reality" -- both realities: When they complain about how the scene is going, they seem simultaneously the fictional characters and the fictional actors playing those characters (whereas they are "really" Pittsburgh actors playing both).

It's delicious. We help create these shifting realities with our willing (dis)belief. The ostensible story of the lovers' dependence is interesting, but that we feel the emotion in spite of the transparency of the fiction is remarkable.

Kudos to the real director, Joanna Lowe of Cup-A-Jo Productions, and to a fine cast of Molly Beth Seremet, Lauren Tassi, Trent Wolfred and Thomas Sterner. If in the next three weeks the festival produces a better play, I can't wait to see it.

The two-hour evening begins with Roger Hobbs' "Not Another Divine Comedy," directed by Naomi Grodin for Open Stage, in which Michael (the always appealing Greg Caridi) finds himself on a subway to Hell guided by Dante (Marcus Muzopappa, playing the great poet as a sort of resigned consigliere).

Hobbs exploits a lot of the jokes you'd expect as well as some you don't, as Michael meets Charon, Jesus and other residents of the after-life (all played by Sara Gaille and Ryan Ben) while the train hurtles past the various circles of Hell. But for all its wit, the play never deals convincingly with its central plot -- Michael's fate.

The middle play is "Starla," a sort of ghost story by Slippery Rock theater prof David Skeele, directed by Ashley Adams for Baldwin Players. A full-of-himself acting teacher (Philip Bower, in a fine, unctuous performance) brings a female undergraduate (Deanna Brookens) to a deserted theater to "work on her monologue." We watch him play the inspirational guru, waiting for the inevitable seduction, and although the scene does go that way, Skeele has an unexpected, darker turn in store.

It does go on rather long before getting down to that surprising turn, but it is full of humor for anyone who's experienced the self-conceit of theater people and theater departments. In fact, this first festival week is a pleasure for theater lovers in general.