Historian Simon Schama ("A History of Britain") plays sleuth -- searching, he says, "not for literal truth, but for poetic truth" -- as he speculates about whether an innocent man was executed for a 154-year-old "Murder at Harvard." The victim was prominent Boston physician-turned-businessman George Parkman, who disappeared on Nov. 23, 1849. Remains thought to be his were found a week later in the Harvard Medical College's basement, and chemistry professor John Webster, who owed Parkman money, was convicted of the crime on the basis of circumstantial evidence.