The Rainbird Pattern (1972) by Victor Canning
Elderly spinster Julia Rainbird, under sessions by medium Blanche Tyler, or "Madame Blanche", promises her a large sum of money to locate her illegitimate nephew Edward Shoebridge. Blanche and her boyfriend, George Lumley, begin making inquiries around their area about the Shoebridges, despite no one knowing where Edward is, or if he is alive.
Meanwhile, Edward Shoebridge, alive and under the pseudonym of "the Trader", has been organising small kidnappings around the area, but is planning a larger score, the Archbishop of Canterbury, whom he will hold for a large ransom.
Wonderfully well-detailed and real plot concerning complex kidnap of topmost Establishment figure. The sheer imaginative weight holds you like a giant electro-magnet.
— The Times, 26/Oct/1972