Well this was a new one to me! The Voynich Manuscript discusses a rather odd document (now held at Yale's Bienecke Library) which seems to be written in some sort of cipher and is accompanied by a series of bizarre illustrations. The work has resisted all attempts to force its secrets, and remains one of those enigmatic historical problems that can serve to either tickle the imagination or drive one totally mad.
Gerry Kennedy and Rob Churchill, English television writers/producers, offer here a readable and useful introduction to the manuscript, its checkered history, the efforts of those who have sought to explain it, and also a grand overview of the various theories which have sprung up around it. Is it an unknown work by the thirteenth-century mystical friar Roger Bacon? Or is it the product of migraine-induced hallucinations? Could it be nothing more than a very elaborate hoax (and if it's a hoax, was it created in the early Renaissance, or the early twentieth century?). Is it possible that humans will ever break its code?
While this book is rather too full of digressions, dead ends and tangents, the manuscript's own power to intrigue kept me going. It is, without a doubt, one of the more fascinating literary mysteries I've read about recently. Not to mention the great cast of book characters who make appearances: Wilfred Voynich (who may have pilfered the manuscript in the first place from an Italian library), Milicent Sowerby, H.P. Kraus, &c. And those extraordinary illustrations ... wow.
There seem to be quite a few Voynich MS-related sites out there, including this one which looks to have some good images. Googling will give you more than you could ever wish for.