National Theatre Live: London Assurance: Grace has agreed to marry Sir Harcourt in return for his financial support of her family. At a house party in her father's place, Harcourt's son Charles also falls in love with Grace. When his father appears on the scene, he has to convince him that there is a case of mistaken identity and he is somebody else. Then Lady Gay Spanker, a married woman also visiting at the house, is persuaded by Charles to seduce his father and thus divert his attention from Grace. Much confusion and scheming ensues.