If I owned this, I would put it on the bookshelf next to The Templar's Secret Island. It's pretty whacked, initially in an amusing sort of way, but then increasingly opaquely. With the Templar island book, the authors build their case very linearly, placing each of the twelve churches in sequence to reveal their Great Secret. Kingdom for a Stage progresses in parallel, and you need a scorebook to keep track of whose son and brother was godfather to John Dee's kids and then married which woman who was also the daughter of this other guy who maintained a theatre troupe.
The book features mysterious geometric drawings, magical numerology, Templars, Rosicrucians, John Dee, Shakespeare, Francis Bacon and his secret society, and, in the very end, a possible mystical marriage between Queen Elizabeth and the Earl of Leicester and a resulting child.
Dame Frances Yates made respectable the study of occult thought in Elizabethan England. Despite the author's numerous invocations of Dame Yates, this is nowhere in her league. Case in point: John Dee has a two-year gap in his diary. The last entry for 1598 is made in Manchester. The next one is in 1600, as he is leaving London. Because John Dee had some noble friends, and because these nobles were interested in and sponsored acting troupes, clearly John Dee was called to London to oversee the construction of the Globe and the Fortune theatres.
It is an excellent example, though, of the kinds of illuminated thoughts that Renaissance occultism invites. By associating numbers, letters, planets, colors, metals, and more, one can find an infinity of hidden correspondences which take on immense significance to the person who has "discovered" them.