Nadine Akkerman's incisive and penetrating Invisible Agents thrusts us into a world of cryptography and steganography, of letters hidden in hairdos and written in invisible inks, of spymasters running double agents and Black Chambers full of codebreakers. In less subtle hands, the narrative could easily run away with the book, leaving the reader with a bracing but facile story of intrigue and adventure. What Akkerman does, though, is far more interesting and difficult: she approaches the material as a spymaster herself, carefully unpeeling the many layers of the archive to reveal the true history of the role women—or “she-intelligencers”—played in early modern English espionage.

Akkerman is not the first to examine the importance of this intelligence, and she makes clear references (and in a few cases, small corrections) to the work of Alan Marshall, David Underdown, and Rachel Weil, among others. But what sets Invisible Agents apart is its almost total focus on women as the gravitational center of the world of secret “intelligence [that] was crucial to domestic security and state formation throughout Europe in the early modern period.” (12). In doing so, Akkerman emphasizes the importance of women to the high political narratives of the British Civil Wars, making a compelling case that we cannot truly understand the period—or, indeed, early modern state formation—without understanding the role of these women.

This is in many ways the best kind of gender history: one that uses the precise tools of gender analysis to reveal a changed (and fuller) landscape of a past that we thought we knew well. But it also owes enormous debts to both literary analysis and material culture, each of which uncovers layers of meaning in the extant archives. Indeed, Akkerman is especially persuasive when deciphering the past, in some cases entirely literally. Her prodigious knowledge of the archives allows her to make connections that have otherwise been overlooked. So, for instance, she turns to a cipher key used by Lady Dysart and the Earl of Inchiquin not just to find letters between the two intelligencers but to discover “other letter writers who were privy to the key but not necessarily part of this conversation” (143). Akkerman unfolds this evidence further, reconstructing an even larger group from the cover addresses of the wider correspondence. She thus exposes a significant network of she-intelligencers and their informants, none of which would have been possible without such archival ingenuity (143–48).

That few of these women have been given the credit they deserve for their work is part of Akkerman's intention in calling them invisible agents; historians and archivists, ignorant of the codes and meanings that were the very craft of these intelligencers, have elided them from the record. To a certain extent, we cannot blame these scholars; as Akkerman notes, the “most effective spies will remain undiscovered” (24). But much of this disregard results from the gender biases of the historians themselves, and Akkerman spends much of the book shattering their assumptions. Elizabeth Alkin did not switch from spy to nurse as a result of rediscovering a “womanly instinct” but because the new profession was an excellent cover for moving between enemy camps without raising suspicion (72–73). Susan Hyde, the sister of the Earl of Clarendon, did not engage in the innocuous domestic chatter that led past editors and archivists to omit it from collections of state papers but instead used “textual codes and material features” to hide significant political intelligence (89–90). And Akkerman convincingly argues that the probable bowdlerization of Anne Halkett's memoirs during a Victorian rebinding of the manuscript has obscured the deeply political meanings of her “True Accountt” (184–88).

This metaphor of invisibility is rather more convincing when talking about the approach of historians than when discussing the attitudes of these women's contemporaries. Indeed, the greatest weakness of the book lies in the strain between repeated claims of contemporaries’ skepticism about the very idea of a she-intelligencer and their reliance on the same. The claim that “people simply refused to believe that women could possibly be included in such plots” (4) is belied by later descriptions of she-intelligencers routinely employed as spies—as well as searched, arrested, imprisoned, and even drowned for espionage. That women were usually underestimated, sometimes ignored, and often able to cloak their activities in domestic disguises is all very plausible; indeed, Akkerman persuasively argues that this could make women the very best spies. But it is only in the conclusion that Akkerman truly reconciles the tension between the desire to protect concepts of womanly purity and the reality of women working in the muddied shadows of political life.

Invisible Agents is at once a fine piece of literary and historical analysis and a methodological tour de force. It is a book that repays careful reading and one that reveals worlds heretofore obscured: by the vagaries of time, by biased archives and analysts, and by the exceptional clandestine skills of the she-intelligencers themselves.