It would be easy for the modern reader to conclude that women had no place in the world of early modern espionage, with a few seventeenth-century women spies identified and then relegated to the footnotes of history. If even the espionage carried out by Susan Hyde, sister of Edward Hyde, Earl of Clarendon, during the turbulent decades of civil strife in Britain can escape the historiographer's gaze, then how many more like her lurk in the archives? Nadine Akkerman's search for an answer to this question has led to the writing of Invisible Agents, the very first study to analyse the role of...