«129. The Viscount's Revenge» by Barbara Cartland

The Marquis of Craigmere, who is one of the most handsome and attractive men in the Beau Monde, is pursued by an exotic and beautiful married woman called Peony Lawson
The Marquis finds this affaire-de-coeur amusing and enjoyable until Peony says that that she intends to tell her husband what they have been doing and ask him for a divorce.
The Marquis is horrified because he was determined never to get married until he is much older and needs to have an heir. He knows, however, that Peony is serious and he will have to be exceedingly clever not to be involved in a scandal that would force him to live abroad for some years.
He is at Royal Ascot and is hoping to win the Gold Cup. He is not successful, but as the race ends he sees the Duke of Hawkhurst, who was a friend of his father's.
The Duke has always been in debt and a way suddenly occurs to the Marquis of saving himself from the horror of Peony's intentions.
He tells the Duke that he wishes to marry his daughter, Natalie, in two days' time. The Duke thinks it strange, but he realises that a very rich son-in-law will save him when he is on the verge of bankruptcy.
However, his daughter Natalie is in love with the charming son of a neighbour, who is far from being a rich man, and she is in despair at the prospect of being married to the Marquis.
Her cousin, Silva, who is beautiful and intelligent, urges her to elope and promises that she will somehow keep the knowledge of it from the Duke until it is too late for him to prevent it.
How Silva arranges for Lady Natalie and the man she loves to set off for Gretna Green and how to save not only her cousin, but also herself from what has been for her a life of misery at the Duke's Castle, she takes her place at the altar.
And the Marquis only discovers the switch when they are on their way to Dover for their honeymoon on his yacht.
Find out what happens next in this intriguing and fast moving love story by BARBARA CARTLAND.