Grace Zaring Stone who is also Ethel Vance and one of the duennas of the ancien regime has written what the publishers call a ""suspense novel of manners"" and what is essentially a high-toned mystery. Paul Prentiss, seventy, takes a young man just out of the service back with him to his home in a small New England town where, under the nasturtiums and marigolds, there are all kinds of latent unpleasantness. They relate to Cordelia, the only one of these old codgers and characters who is very wealthy, and Avril, the young girl who has married Cordelia's brother, and dear deadly Cara, dear dead Cara. . . . All of this goes down very easily even if it comes right back up again, but the ladies will like the author, the ambience and the many, many assumptions of guilt and innocence.