The 21 Lessons of Merlyn: A Study in Druid Magic and Lore - Douglas Monroe (Llewellyn Publications, 1992).
This has got to be one of the stupidest Neo Pagan books ever; it's hands down the stupidest ostensibly
According to Monroe's Introduction, the druids made books of leaves, with each leaf representing a character of ogham. Ogham is a late fifth century creation, one that's very definitely based on Roman writing and letters. Most of his information about ogham, by the way, is based on Robert Graves book, The White Goddess, a book Graves later essentially disowned, and one that's full of errors.
Monroe states that druids were vegetarian (p. 42). This is absolutely not true; for one thing, the climate they lived in was not one that was conducive to vegetarians; they would have starved. For another, the laws about precedence at the shared cauldron specifically discuss fork-rights, and meat, for druids and poets. For a third, two of the few druidic rituals we have specifically require that the druids eat meat during the ritual.
According to Monroe, Easter is the Gaelic festival of the Goddess Ishtar. This is so idiotic I hardly know where to begin. Easter is derived from the same root as "East," rather obviously. Middle English ester, Old English astre, derived from the Proto Indo-European root *aus-, to shine. There's no connection, at all, with Ishtar, who is a deity of the Sumero-Babylonian region, and is of Afro-Asiatic, and not even possibly related to a Celtic deity. In fact, he keeps getting references to Celtic deities wrong; for instance, he thinks the Roman god of doors, Janus, is Celtic.
Then there's the rampant misogyny. Monroe clearly has certain issues around women and sexuality (and by the way, the pictures of the young blond boy scattered throughout, and Monroe's references to children are seriously creepy). According to Monroe's chapter on male and female druids (chapter 12), male druids were required to be celibate. Given the numbers of druids who had children in the myths, the genealogies, and the law codes, and the rules about inheritance, this is absolutely false. He describes female druids having sex in order to take power from men, since they have none of their own. This is far more deeply revelatory regarding Monroe's own issues than anything approaching accuracy regarding druids. It's particularly odd given that in the Celtic myths in Irish and Welsh, the power of sovereignty is conferred by a woman upon a man.
Monroe has a bizarre mixture of modern Neo Pagan bits, fake Irish and Welsh from movies, and dangerous herbal lore—he suggests drinking absinthe, without going into the details about which absinthe is and is not safe, he suggests ingesting mistletoe berries, and, rather hilariously, has pumpkins growing in the Celtic regions of Europe as a native, medieval plant.
According to Monroe, this tome of druid wisdom is from the sixteenth century Welsh manuscript called the Book of Pheryllt. This is untrue. The manuscript is a forgery, and Monroe, who can't even read Modern Welsh, certainly couldn't read a sixteenth century copy of an early Middle or Old Welsh text. Still not convinced? I'm a Celticist, rather than a Neo Pagan, but here's Ellen Evert Hopman,
Run away from this book. It's full of stupidity.