This novel has all of the characteristics that make Storm Constantine such a compelling author. The world she creates is conflated from the Sumarian creation myth of Enlil and Ninlil with the ancient Kabbalah and more recent Christian Cabbalistic apocryphal influences, especially the myths of Shemyaza and the Grigori and even Enochian magic. Without any knowledge of these myths, the world seems real and almost likely. It would make a great neo-pagan spiritual system! With basic knowledge of these myths it is an amazing accomplishment bringing them alive in modern Britain.
Her characters are delightful and most could easily find one or more to identify with. The prose or word-smithing it typical of Storm, that is flowing, exciting, well-paced and with enough esoterica to allow for googling and wiki-ing for those so inclined. It works on multiple levels and can be read as a great story, as a great story with allegorical themes or—This 1st book of this trilogy can open an entire new world for you to explore from our historical and mythic past, right back to the beginning of human writing. Best, IMO, to read it all all levels.
I had trouble genre-izing the novel. It typically falls into fantasy or dark or gothic fantasy. But I think it more than those so included it as mythic fantasy where I think it best fits. It is very much about our historical and mythic basis.
I’d suggest that at he very least one read a translation of Enlil and Ninlil— http://etcsl.orinst.ox.ac.uk/section1… —look up Grigori and Shemyaza