Holmes and Russell return home to Sussex to discover that Laurie King has made a major addition to general Holmes canon - a son. Some might be put off by this, but that element works well. Holmes has always been a mysterious character in his personal life, concealing what emotion he feels, even in the original Conan Doyle stories.
From here the hunt for a daughter-in-law and potential grandchild lead them into the path of mysterious cult. Bodies turn up at prehistoric sites and the sacrifices that the cult alludes to might be more than merely spiritual. The Aleister Crowley style shenanigans fit well with both the Holmes stories more gothic elements and with the spirit of the mid-1920s when odd religious movements flourished (much like current 'new age' beliefs). But the book is actually somewhat lacking in atmosphere. The religious movement never develops into the ominous force it might.
Instead, the threat is contained to just one individual within the cult. The motivation for what he does remains unclear. We are told that the thoughts behind the religious movement are muddled at times and that details are fudged in terms of a greater truth - but that appears to be a good excuse to allow King to do whatever she wishes. Quotes from the religious text at the start of each chapter add some flavour but never really give any sense of what the cults and its leader's aims are. An interest in Norse myth is bad, we are told by an expert, because that means 'Ragnarok, of course' - suggesting a desire to usher in the end of the world - but the Vikings were far from the only people to believe in a final apocalypse (Christianity has its own fine and scary vision of the end of the world); why should anyone leap to that assumption? The Norse elements do not appear otherwise to be significant. It feels just a little half baked.
The problems are broader: Holmes spends much of the book out of the way investigating other aspects of the case. But Holmes is always the star turn in any book he appears in and Russell's investigation meanders somewhat. When he does appear he is often reduced to either smoking his pipe but achieving little or, alternatively, acting as something of a deus ex machina, wrapping up elements just a little too easily.
There is a lengthy sub-plot at the beginning of the book about a mysteriously failed bee-hive. One might hope that the solution of this would have some bearing on the main mystery but by the end of the book it appeared not have done. Perhaps this will be remedied in the next part, 'The God of the Hive'.
The book is entirely readable - and I will certainly go on to the next part - but it fails to completely satisfy. King's books in general do not seem to have the feeling of being a well crafted machine that some mystery stories do - a style that the original Holmes stories helped to create. That is a shame, particularly here where the story seemed to promise a lot and never totally delivered.