I wrote a few days ago about watching the televised version of this story. I had only seen the first half when I wrote - I was in for a surprise in the second half, when the story became almost a complete reversal of the original novel. It is clear that the relationship between the written word and the dramatised word is fast approaching zero.
Naturally, I had to read the novel again, especially as I remembered it as being one of the best of the early Banks novels - an arbitrary line drawn by the arrival of Annie Cabbot. This book features Superintendent Gristhorpe (Banks' superior) in a more active role than usual. It also mentions towards the beginning how Gristhorpe, as a young uniformed police officer, took parts in searches for the victims of the Moors Murders, and how he heard tapes of the perpetrators torturing children to the sound of carols - which turned him permanently off music from then on, always pretending to be tone deaf.
Which makes it very strange to read at the beginning of chapter 12 that "Besides, Gristhorpe was tone deaf; for all his learning, he couldn't appreciate music". This is a sentence which must have been written in a reflex manner; it's always something that comes up when Gristhorpe is mentioned. But as we know - having already read so at the beginning of the book - Gristhorpe is not tone deaf, he just does not like listening to music. This is a sentence which should have been removed by a sharp editor.