Mr. Carter, continuing to feature his wife Marjorie Allingham's Mr. Campion, assigns him to the case of a defected Russian Kopeck (the equivalent of a farthing). He's a physicist with a formula which lends a euphoric inducement to dying, and when last seen he was at an elegant stately home offering chamber music and haute cuisine to its paying weekend guests. . . . Good humored, high handed legerdemain for the retinue once established and still enduring.