The Chalon Heads: Barry MaitlandBrock and Kolla 4. When Scotland Yard detectives David Brock and Kathy Kolla are summoned to Cabot's, a venerable dealer of rare stamps, they expect a simple case of theft and a pleasant digression from the usual sort of wrongdoing encountered in the Serious Crime Branch. Instead, they find themselves on the trail of an extortionist when they learn that the wife of Sammy China, an unsavory figure from Brock's past, has been kidnapped. The only clue is