In this article Professor Hyde examines in detail the use of industrial spies at a large Michigan copper mine in the early twentieth century. While many historians have argued that labor spies were powerful weapons effectively used by employers in their struggles with workers, Hyde finds in his case study of the Quincy Mining Company that spies were seldom useful in providing important labor intelligence. Instead, they inadvertently provided top management with valuable information about underground working conditions and the performance of foremen and petty bosses.