When the recently widowed Mrs. Emmeline Lucas (Lucia to her friends) desires a change of scene she determines on the picturesque seaside town of Tilling for an extended break. There, with her ever-faithful friend and accomplice George Pillson in tow, she sets forth to wrest the reins of Tilling society from Miss Elizabeth Mapp. But the Machiavellian Lucia has not reckoned on the indomitable Mapp, who has no intention of giving up her supremacy. Has Lucia at last met her match?
Battle lines are swiftly drawn as the ladies strive to outdo each other, using invitations to delightful garden parties and, above all, the recipe for 'Lobster a la Riseholme' as their deadly weapons (to the fascinated horror of their friends), for the position of doyenne of Tilling.