In the summer of 1999, in the tiny west Texas town of Tulia, thirty-nine people, almost all of them black, were arrested and charged with dealing powdered cocaine. The operation, a federally-funded investigation performed in cooperation with the local authorities, was based on the work of one notoriously unreliable undercover officer. At trial, the prosecution relied almost solely on the uncorroborated, and contradictory, testimony of that officer, Tom Coleman. Despite the flimsiness of the evidence against them, virtually all of the defendants were convicted and given sentences as high as...