There are lessons to be learned for retired teacher Hildegarde Withers when a society murder reveals a love triangle gone bad.   The war in Europe is over, and America's fighting men are coming home. Lieutenant Pat Montague spent the war dreaming of a return to his beloved: society princess Helen Abbott. But when Uncle Sam finally lets him go, Pat finds that Helen has become Mrs. Huntley Cairns, and he has nothing to return to at all.   He goes to see Helen at the Cairns mansion, only to stumble upon his rival's murdered corpse. The jealous soldier is the obvious suspect, but Pat's friends know he is innocent, and entreat Hildegarde Withers—elementary school teacher and talented sleuth—to clear his name. Huntley was rumored to be involved in the black market, and Miss Withers soon discovers his killer was far more sinister than a soldier with a grudge.   Miss Withers Regrets is part of the Hildegarde Withers Mysteries series, which also includes The Penguin Pool Murder and Murder on the Blackboard.