POUGHKEEPSIE, N.Y. - It sounds like a TV show: Don Foster, a mild-mannered English professor, makes time beteween teaching college kids Shakespeare to solve mysteries.

He sniffs out a long-lost poem by the immortal Bard. He unmasks a best-selling author who anonymously disparaged the president. And he takes it on the chin a couple of times along the way.

The twist is that Foster is not a gumshoe in the typical sense.

The 50-year-old Vassar College professor is a literary detective. He analyzes writings - things like poems, books and ransom notes - in order to identify the author. He has looked for revelatory clues in the dark ramblings of the Unabomber, the girlish prose of Monica Lewinsky, even the beloved holiday verse beginning, "Twas the night before Christmas."

The results have been some dramatic pronouncements, a bit of controversy and now a book summing up the professor's high-profile sideline, "Author Unknown: On the Trail of Anonymous." The book also serves as an extended argument by Foster that an individual's writing is like a fingerprint - a mark of identity that shows through in the words we choose to use and the way that we use them.

"In my opinion, the kind of evidence that a text supplies is more reliable than eyewitness testimony," Foster says during an interview in his office. "An eyewitness can forget or lie or equivocate or leave the country or become ill or mistake one face for another."

Foster seems at ease in the cloistered confines of Vassar's Hudson Valley campus. He banters easily with a class of sophomroes over cuckolding jokes in "Much Ado About Nothing." The married father of two sons is soft-spoken, self-deprecating and can reel off long quotes from Shakespeare in conversation. Academia would probably remain his lone passion today if not for the pull of a certain literary mystery.

"I never wanted to become Mr. Attribution," he says. "It just sort of happened to me."