by Knopf, $12.95. The theme of Mr. Bogarde’s novel is pretense—the contrast between what people really are and the roles they choose to act in the world. The world, in this case, is a luxurious Riviera villa where assorted characters play out a bittersweet harlequinade. The hero and heroine are likable young people with just enough of a naughty streak to maintain suspense. The dialogue is clever, and the book is enticing reading all the way..