I appreciate that this was written in 1981, however I find many parts of the plot and writing unbelievable.
I grew up in this period, and am from Devon and know Dartmoor and the Southwest very well so several parts bothered me, from an early morning walk through Exeter, that the main character takes before breakfast, which in reality would have taken four hours to complete, to a Forensic Scientist, in those days, commuting between Plymouth and Bristol each day for work.
I also found the character of Crow and the final scene rather unbelievable. He's brought in as an outside eye to re-start an investigation from scratch yet appears to be as narrow-minded as the original Detectives. Sorry, that doesn't work.