The plot (without spoilers): important people are getting kidnapped, and those in pursuit seem powerless th stop, or even trace, the kidnappers. Chance intersection of paths of a psychic medium and her investigative sidekick with an old lady muddies the waters - or clears them?
The writer: Victor Canning wrote many noverls, often with a thriller plot in the 1950-1970s. This one is from 1972.
My opinion: Canning has a very distinct voic - I don't think you should read his books too close together! He can be a bit samey on the moral musings of his characters, and on their personal thoughts. On the other hand, he is very good wih nature; his plots are loose but gripping, his personalities well fleshed out... enjoyable, light-hearted romp (if violent in places), and a good puzzle-mystery!