The earliest mention of Dr. Faustus observes that he studied magic in Kraków, Láng points out, where magic had been taught openly and thus created a reputation for the city and its university (but Láng observes that the historical Faustus probably never went there). He also tells us about one Nicholas of Poland who, rejecting his Montpellier medical training from over twenty years previously (around 1250), recommended for general health as well as various ailments frogs, toads, and snakes, often desiccated, then pulverized in a mortar, and mixed with liquids. The peculiarity of these prescriptions (to his learned contemporaries and to us) is not the point, nor is the fact that the prescriptions have nothing to do with magic--rather, it is that Nicholas departed from learned reliance on authority and endeavored to rely on experience, yet the experimenta of magical texts were largely based not on experience but on authority. In the fourteenth century, one Elisabeth addressed God by over a dozen different names, praying that her husband might love and obey her, and Theoderic duly signed the magical prayer along with her. By the fifteenth century, the whole of "Central Europe" (Bohemia, Hungary, and Poland) apparently had a liberal tolerance for magic that extended even to legal indifference, and Láng indicates this might be more general, finding a "positivization" from Augustine through William of Auvergne and the anonymous Speculum astronomiae, and to two late-medieval texts, one extant in Prague and Münich and the other copied in Kraków in 1488.
There are three formal main parts to the book, but the first two are really one unit: "Magic" is a discussion of what it is and how magical works might be classified, and "Texts and Handbooks" looks somewhat at the manuscripts but more so at six classes or genres of texts (excluding astrology), with a chapter devoted to each. First is "Natural Magic," by which one can affect things through their secret but natural virtues because "different parts of the world are in occult correspondence with each other" (36). Láng describes the main lines of natural magic by means of the Experimenta Alberti, the Kyranides, and the Secreta secretorum, which circulated in manuscripts largely of medical and astrological interests. The technology of warfare also extended to magic, here illustrated by the Bellifortis of the German mercenary Conrad Kyeser, which mixes engineering and invention with rings, amulets, and invocations of demons.
Next is talismanic "Image Magic," which had an uncertain relationship with astrology but was not clearly natural magic or ritual magic (this involving demons and thus sometimes described as demonic magic). These texts come from Arabic ones translated into Latin in Spain (such as the Picatrix) and focus on a talisman or seal, the imago or ymago. To illustrate, Láng turns to Biblioteka Jagiellońska MS 793, containing astrological and medical texts as well as several texts of image magic: De septem quadraturis planetarum seu quadrati magici,  Thebit ben Corat's De imaginibus, the Picatrix (partial but unique in being illustrated), and other works. After some background on Hermetica, various "Operative Hermetic Talismans" are discussed,  such as the Liber runarum, which actually uses Scandinavian runes, and four talismanic texts.
Third is "Divination with Diagrams." The future, it was thought, could be predicted and occult secrets obtained by geomancy (interpreting patterns made from points on parchment or soil), palmistry or chiromancy, and other means, all of which required illustration in the manuscripts. For this reason, the chapter has an excursus added on pictorial elements like tree diagrams, circles and rotae, and mystic alphabets. Fourth, "Alchemy," apparently had a robust local development in Central Europe, producing even one work based on the organization of the mass. Its popularity extended beyond academics to the clergy (regular and secular), given manuscript evidence and an alchemical laboratory found in a fireproof room in a chapel. Finally, "Ritual Magic and Crystallomancy" involves methods of invoking supernatural agents; for example, the Prayer Book of King Wladislas of Poland (Bodleian Library MS Rawl. liturg. d. 6) and similar works of notorial arts, which promise knowledge and wisdom through rituals, prayers, and invocations of angels, the Virgin, and God, with or without a crystal, mirror, basin of water, or other device.
The third main part turns to "Readers and Collectors" in their clerical, courtly, and university contexts. Archbishops and preachers railed against necromancers, of course, but some manuscripts with monastic connections contain dubious texts, such as a Bible with two Hungarian experimenta or the more common scientific or medical compendia with magic texts. Royal libraries contained many manuscripts whose contents could easily include such works, but certainly the court took advantage of learned individuals (as well as alchemists) whose practices at times could lead to their being described as magicians, such as Henry the Bohemian, astrologer and accused Hussite and possessor of forbidden books, imprisoned for life rather than executed, thanks to protection by the court and his popularity among the citizens of Kraków. Obviously, some of those learned individuals were related to the universities, where deep interests in medicine, astronomy, and astrology led to books including magical texts of many kinds.
Thankfully, mistakes are rare (e.g., "single points, .we" p. 126, "deliberated" for liberatus est p. 195, a period where some text seems lost in p. 192 n. 4, and "The case...provide" p. 225) and infelicities of phrasing are infrequent. Rather, we should be impressed by Benedek Láng's linguistic skills: the generous footnotes display English, French, Italian, Latin, German, Hungarian, Polish, and other languages underlying the extensive research undertaken to produce this tome, and while English translations are given in the text, the footnotes largely supply the originals for comparison and reference, and they translate titles of references in languages Anglophone readers are not likely to know. He also provides a goodly number of illustrations, though most are simply mentioned in passing. In all, Unlocked Books is a pleasant, informative read that illuminates magical texts, manuscripts, and social uses in Central Europe and well beyond.
1. I published a version of this in 1998, at which time I found no other copies. Since then, however, at least about a dozen copies have been uncovered and are being edited by Sophie Page or Vittoria Perrone Compagni for the Hermes Latinus portion of the Corpus Christianorum, Continuatio Mediaevalis.
2. The URL given for the Hermes Latinus web site on p. 104 n. 54 should probably be http://www.tecnopublish.com/HermesLatinus/