Tricky and even a bit morbid in his past few (always readable) thrillers, Canning now returns with the simplest, most appealingly old-fashioned sort of suspense. The hero here is a sterling lad--London's motherless, 14-year-old Peter Courtney--who has one of those total-recall trick memories so useful in espionage fiction. And it isn't long before British Intelligence hears of Peter's prowess (his bookstore-owner dad Frank has been showing Peter off, for a fee, at private parties): they persuade Frank to take Peter to France, where the Conte de Servais is eager to pass along a list of French and British agents who've secretly sold out to Russia. But, though the Conte, as planned, recites his piece to Peter--who has no idea of its significance--things soon become tense. The Conte is murdered: there's a traitor high up in the British spy office; and when Frank and Peter return to London, a domestic crisis totally distracts them from getting Peter promptly deprogrammed: Frank learns that his second wife Joan is a bigamist (he catches her in bed with hubby #1), so father and son take off on a train to Penzance to recuperate from the shock. British Intelligence is looking for them, of course. So is a pudgy, creepy hired-killer. And Frank eventually realizes he'd better make contact with Intelligence--though he and Peter are finding peace and closer ties while staying in a trailer on the estate of lovely recluse Lady Diana. A hand-me-down plot? Yes, mostly. But Canning times his inventive final twists perfectly; he has two irresistible, imperiled heroes in conscience-stricken Frank and pure-hearted, train-loving Peter; and his easy, warm-hearted charm is on page-by-page display (though US readers may wince at genial references to ""a darky"" and ""coloured boys""). A blithe throwback--with a Buchan plot, a boy-scout sensibility, and enough relaxed brio to move it along with endearing assurance.