Released right before Remembrance Day, David O’Keefe’s new book, One Day in August, is an account of the Allies’ tragic raid at Dieppe with a twist—it introduces new evidence that claims to solve an important World War II mystery and put to rest a legacy of unease and confusion.

Until now, history has remembered Dieppe (Operation Jubilee) as the most catastrophic amphibious attack ever carried out. The intrigue surrounding the raid is the apparent lack of rationale behind the entire mission—it was “an operation seemingly devoid of tangible purpose and intent.” As a result, a “legacy of sorrow, bitterness, and recrimination has developed to frame the collective Canadian memory.” One Day in August delivers on its promise to finally address the burning question: why?

Jubilee was ultimately driven by the “four-rotor crisis”—the desperate necessity for British Intelligence to crack Germany’s Enigma code, which was encrypted through the Enigma machines as a means of delivering secret messages. The machines had recently been upgraded from a three to four rotors system, introducing an added layer of complexity that was nearly impossible to decode. For intelligence analysts working on Ultra at Bletchley Park headquarters, the only way to crack the code was to obtain, via “pinch” operations, various cheat-codes that could unlock top-secret Enigma messages. The raid at Dieppe was meant to be that “pinch.”

O’Keefe’s narrative is divided into two sections. First, he introduces the extensive British intelligence organization, whose inner workings must be intimately understood to appreciate the anxiety to decipher Enigma—even Winston Churchill is described as having a sort of addiction to his daily dose of Ultra-secret intelligence. O’Keefe does justice to this fascinating area of British history; his use of primary sources (including 100,000 pages of archival material) brings to life the various personalities of WWII—among them Ian Fleming, the creator of James Bond, and also a competent British Intelligence officer in his own right.

Fleming turns out to be the key to unlocking the Dieppe puzzle, reappearing in the second part when O’Keefe showcases his skill as a military historian. The overview of Operation Jubilee from conception to conclusion is explained with precision and detail. Now, we can understand Dieppe for what it truly was—even if many who fought that day could not. Had they been successful, they would have obtained material that “in cryptographic terms was the proverbial Holy Grail.” Fleming, waiting on board one of the ships to bring the pinched codes back to Bletchley Park, was the final link for exposing Dieppe as a veiled pinch operation.

Pinches were required so that there appeared to be another driving force behind the raids, in order to prevent German suspicion of the missions’ true objectives. Only information as sensitive as Enigma codes would have warranted the loss of so many lives, but since no one could know that crucial reason, the staggering loss of life has understandably confused and distressed the world for so long. With this new information, there is finally an explanation for the massacre of August 19, 1942.

The most serious shortcoming of One Day in August is O’Keefe’s clear sense of pride in his work. Evidently, he has invested many years into the book and is excited to have solved a WWII mystery, but his personal feelings at times infringe on this serious non-fiction in a way that is almost ludicrous. In addition, there is a redundancy of explanations; this leads to the sense that at best, O’Keefe was condescending to us as readers, or worse, that he wrote haphazardly and then failed to edit closely enough to smooth out overlaps in information. These faults detracted from an otherwise exceptionally well-written work.

One Day in August is a tremendous addition to the legacy of World War II history, with the added excitement of solving a mystery and the satisfaction of resolving decades of national unease. It proves that WWII remains a dynamic and fascinating part of history that we may never completely understand. For all lovers of history, cryptography, warfare, intelligence, or even conspiracy theories, O’Keefe’s work definitely deserves a read.