The Consecrated Little Book of Black Venus, attributed to John Dee, presents us with a curious puzzle in the history of magical manuscripts. It instructs the reader how to perform the "Horn of Venus", which at first seems a lengthy but straightforward rite in the tradition of Henry Cornelius Agrippa. "Dee" tells us that this "Horn" might be used for "lifting hidden treasures, for Navigating, Trade, war, and other ways likewise where the Spirit can be of service to you " and instructs the reader, repeatedly, to make all preparations on the day and hours of Venus, and to perform the rite itself only during these hours. We might suspect this "Horn" describes a not-so-veiled tantric working, also appropriate to the days and hours of Venus. But then why write the book on Saturday, which would seem a quite inauspicious day for most of these activities?