What is the main conflict in A Handful of Dust by Evelyn Waugh?

Tony and Brenda Last are a young married couple who have been together for eight years. The have a son named John Andrew and they live on a wealthy estate called Hetton. The estate is in England, two hours outside of London. One weekend, a young man named John Beaver holds Tony to a casual invitation made for him to visit Hetton. Brenda meets Beaver for the first time and is attracted to him. At Hetton, Brenda has been cut off from the social scene she once enjoyed in London.