Dying To Tell by Robert Goddard

Lance Bradley, idling his life away in Somerset, suddenly receives a call for help from the eccentric sister of his old friend Rupert Alder. Rupe appears to have vanished without trace. Reluctantly, Lance goes to London where he discovers that Rupe's employers want him tried for fraud. A Japanese businessman claims he has stolen a document of huge importance. And Rupe has hired a private detective to try and trace an American called Townley, who was involved in a mysterious death thirty years before.