This is a lively and compact biography of P. M. S. Blackett, one of the most brilliant and controversial physicists of the twentieth century. Nobel laureate, leader of operational research during the Second World War, scientific advisor to the British government, President of the Royal Society, member of the House of Lords, Blackett was also denounced as a Stalinist apologist for opposing American and British development of atomic weapons, subjected to FBI surveillance, and named as a fellow traveler on George Orwell's infamous list.