How do we construct a metric for massive human violence? Much has been written about the violent events of 1641, variously termed massacre or rebellion by those who have discussed them. In this contribution to a new Wisconsin series, a young Irish scholar thoughtfully examines a historiography now extending over almost half a millennium. An eminent Tudor historian of the mid-twentieth century once inveighed against studying ‘historians instead of history’ but, as Gibney illustrates, our history-writing predecessors constitute a screen between us and von Ranke's ‘wie es eigentlich gewesen ist’. We must peel back the layers of the onion. It is more difficult when the subject is an outburst of savagery such as is frequent and widespread in human history. Cold facts are rarely obtainable. In the case of 1641 their best approximation is contained in the remarkable thirty-one volumes of manuscript depositions collected at the time, and preserved since 1741 in the Library of Trinity College, Dublin. Voluminous, often illegible, repetitive, contradictory and confusing, they have now, at great expense, been published both on line and in hard copy, so that interested parties, lay or academic, can confront their puzzles. Gibney provides the history of the controversies over the depositions, and of their frequent hijacking for sectarian or political purposes. Building on the researches of an American scholar, Walter Love, who died mid-career in 1966, Gibney began with Love's papers, drafts and notes, which were bequeathed to the Trinity College Library, where they lay unused for nearly forty years. Love took historiography seriously. Following the thread of his interrupted effort, Gibney chronicles the ‘shadow’ cast by the atrocities (committed by both Catholics and Protestants) in 1641 and the winter of 1642. The details of who did what to whom, the dark heart of the matter, remain obscure, and the new accessibility of the depositions may not bring resolution. If the number of men, women and children killed was in the thousands rather than the tens or hundreds of thousands asserted by Sir John Temple and his successors, the sectarian fires may still smoulder? The admirable hope of Gibney's book, and of the ambitious project of publishing the depositions, is that a more consensual and less controversial version of events will have an ecumenical effect. In any case The shadow of a year is a useful, well-written and satisfying guide to the uses and mis-uses of what remains a central tragedy of Irish history.