Marriage is many things, but uncomplicated isnt one of them. Even a seemingly happy, stable couple may have unresolved issues and secrets that are dry tinder just waiting for a flame; and in Roger Rueffs play So Many Words, that spark comes in the beguiling form of an attractive young woman who Stanley (Paul Custodio), a married and moderately successful writer, meets on a plane. It turns out shes a fan of his work, and this leads to unexpected temptation. And that leads to problems with his wife Katherine. According to director Doug Staley, the plays a demonstration of a fundamental truth: You never know what goes on inside a marriagesometimes even if its yours. Staley admits hes wanted to produce the play since reading it six years ago, but it wasnt until he thought of casting his Theater Schmeater colleague Teri Mathews in the crucial role of Katherine that it all fell into place. Ive had a feeling that the parts she was getting really werent that challenging for her, he says, referring to her generally small, comic, scene-stealing character roles. As to what shell do in this drama (through Dec. 6), weve got high hopes. JOHN LONGENBAUGH [Also see Kevin Phinney's review here.] Theater Schmeater, 1500 Summit Ave., 324- 5801, www.schmeater.org. $15$18. 8 p.m. Thurs.-Sat. (except T-giving). Ends Dec. 6.