I've said so much already in praise of this trilogy that all I can really add, having now finished the third book, is PLEASE do read these three books! This one, designed to be read last, goes back in time to the 1950s, so about 20 years before the middle volume. David Byfield, the narrator of that book, is here a young priest and teaching at a theological college in a cathedral town. Married to the beautiful Janet and the father of four-year-old Rosie, he is viewed in this novel through the eyes of the narrator, Wendy Appleyard, who finds him cold but very sexy, and describes him as looking like the young Laurence Olivier. Wendy is a most wonderfully drawn character -- anybody who thinks male authors can't create female narrative voices should read this book. Separated from her charming, feckless husband Henry after surprising him in flagrante on a beach with someone she describes as the Hairy Widow (and possessing a snapshot of the event in case her resolve weakens), Wendy has come to stay with her schoolfriend Janet while she tries to decide what to do with her new single life. Witty, cynical, somewhat jaded by the rackety life she lived during her marriage, given to numerous nips of gin in the privacy of her bedroom, she nevertheless has a soft heart and feels for Janet who is coping not only with her intelligent, uncommunicative husband and her rather strange and difficult small daughter but with her ageing father who is descending fast into what today we would know as Alzheimer's. Bored with doing nothing much, she allows herself to be talked into taking a job cataloguing the Cathedral library, and becomes fascinated by the life and poetry of the mysterious Canon Francis Youlgreave, who, she soon discovers, was dismissed from his post at the Cathedral in the early 1900s for some unspecified but clearly very worrying and disturbing misdemeanours. There are still people alive fifty years later who remember Youlgreave and the events of the time, though everyone seems surprisingly unwilling to talk about them. Increasingly drawn to delving into this mysterious and threatening past, which appears to be reaching out and affecting the present day, she is also disturbed by the reappearance in her life of Henry, apparently reformed and wanting to give their marriage another chance. Both what she finally uncovers about the past and a series of grim events which take place in the present seem to raise unanswerable questions about the nature and origin of evil. They also, of course, finally make complete sense of many of the developments in the later two books.
There is an extremely good and perceptive review of this trilogy by Adele Geras on Andrew Taylor's website. Here's a quotation from her final paragraph:
There is murder, and worse than murder. What makes these books different from many others is that the moral dimension of the crimes is examined, and discussed and emphasized. The physicality of what happens is not glossed over, but it isn't gruesomely and unnecessarily dwelt on in hideous detail. The effect of not knowing is sometimes much worse than the unvarnished facts. Monsters are only scary when we have to guess at them. When they are revealed, we flinch and hide our eyes, but eventually we can grow used to anything, and we do.