Williams had a genius for choosing strange themes for novels, making them believably suggestive of spiritual truths. All Hallows' Eve is the story of a man & woman whose love was so great it could bridge the gap of death; of evil so terrible as to be unmentionable, of a vision so beautiful it must be true.
For an account of Williams' views of the relations between dead & living we turn to his final novels, Descent into Hell ('37) & All Hallows’ Eve ('45), which some claim to be the most sustained & exhaustive ghost stories in English literature. In them the dead are among the protagonists, active within their own world, coexistent with that of the living. His ghosts are nothing like the malign creatures who pounce upon their victims in the tales of M.R. James; they bear more resemblance to those portrayed by Margaret Olliphant or R.H. Benson, beings who exist in the world of the dead, who find themselves drawn back to expiate a sin or who make contact, extratemporally, with those among the living who can help them. But where he differs from writers such as these is in his portrayal of a world of supernatural moral law governing the interaction between two levels of being. For him the living & the dead exist within a single spiritual realm. He describes his supernatural world with extraordinary particularity. Instead of obtruding the ghostly element upon the life of everyday, he assumes that life into the supernatural dimension. It's impossible to banish his phantoms from our own world, because we find ourselves inhabiting theirs, subject to its laws. This is made clear in All Hallows’ Eve, completed shortly before his death. In this strangest of all his novels he returns to his earlier concern with the validity & true nature of spiritual power.