In The Last Crusade, Gerald McKnight examines the Poor People's Campaign, the last large-scale demonstration of civil rights-era America, and the systematic efforts of FBI director J. Edgar Hoover and his executive officers to subvert King's ambitious effort to force the federal government to live up to its promises of a Great Society. The book also looks at King's last days as he helped Memphis sanitation workers in their labor-cum-civil rights struggle with a recalcitrant and racist city government.

Although there is no persuasive evidence that the FBI and the Memphis police conspired to assassinate King, McKnight marshals evidence to show that neither agency was blameless.

The conventional view of the Poor People's Campaign is that it was a self-inflicted failure. The blame rested squarely on the shoulders of the second raters of the Southern Christian Leadership Conference who failed to fill the leadership vacuum after King's assassination. But, as McKnight shows, there was a hidden, dark counterpoint to the accepted version - namely, the triumph of the 1960s American surveillance state and its repressive power and flagrant violation of protected freedoms.

In fact, whatever the FBI wanted to do to disrupt the Campaign, it did, aided and abetted by local police agencies and elements of the federal government, including military intelligence.