Imagine a series of books, like Ukrainian nesting dolls, whose parallel plots lead the reader further and further back in time. And then imagine that the characters depicted in those books are real people who discover the books and are unnerved to read about themselves, as well as others leading parallel lives. That is the original premise of Canadian playwright Jayson McDonald's Jigsaw, an enjoyable mystery receiving its U.S. debut at the Wings Theater. Alas, the play, which McDonald also directed, staggers under this complex structure while recycling one too many horror genre clich