An interesting book for people who practice enochian to say the least. This book concentrates solely on the sigillum, it's form and function, the invocation of the angels in it, and Campbells reformed version of it. Mainly the fact that he goes very deep into the form of the seal gives you a very good understanding of the different forces at play in it. He also gives a ritual for contacting the intelligences within it.
After this comes the main course of the book, where he provides first a "corrected" version of the seal, that by his logic would be more harmonious than the original, and after that finds out if it can be further "enhanced". Agree with his new versions or not, this part can be very enlightening and tears down a bit of the thought that the Sigillum would/should be immovable.
It's a short book, but a good read. A rarity since it has some new information and some actual thought behind it instead of rehashing old material into just another "enochian for dummies" book. Get it while you can, its print is limited to 777 copies.