SEP readers -- who've missed this one -- will be entertained at finding the Post editors and the famous entrance to the building which houses the Curtiz' publications the setting and participants in Lesile Ford's latest colonel Primrose item. The mystery involves the inside history -- the skeleton in the family cupboard -- of a fine old Philadelphia family. Misunderstandings -- shielding the wrong people -- etc. combine to make confusion wa confended. But Mrs. Lathan her share and the colonel upsets -- official procedure and romance plays its part (yes, even to the long- proposel).