It seems unlikely that George Judd, an old duffer who fishes on the Thames, should have died of ""natural causes"" and Peter Blair, on a small cruiser, is assigned to look into this as well as the activities at nearby Hastings House, a think-tank villa for the upper echelon of British Scientific Engineering. Before he's through, Blair is in and out of cold water. . . . Classic modern proceeding with a specificity of detail that brings in the incontrovertible conclusion at a pleasantly slower change of pace.