1908: Edith, youngest daughter of Bishop Bridgenorth, is about to be married. Her uncle General Boxer Bridgenorth, will give her away, as he has all her sisters. As at all the other weddings he proposes to Lesbia Grantham, the bride's aunt, who refuses him for the "tenth and last" time. Lesbia wants a family, but not a husband who smokes and is as untidy as the general. The General is soon shocked to find that his disreputable brother Reginald will be at the wedding. Reginald was recently divorced by his wife for assaulting her and for his adultery with a prostitute. Even more distressingly, his ex-wife Leo is coming too. When the divorcees arrive they are not at all embarrassed. It seems that Leo and her ex-husband arranged the "assault" and the "prostitute" so that they could separate without any blame attaching to Leo, who wishes to marry another man - John Hotchkiss.
However problems arise when the bride refuses to leave her room. She says she is reading a pamphlet on marriage! Apparently Cecil Sykes, her husband-to-be, is also reading a pamphlet. Both refuse to go to the church until they are finished. The couple finally emerge from their rooms. It seems that the pamphlets have revealed to them the dangers of marriage. She has learned that if her husband becomes a criminal lunatic she cannot divorce him. He has learned that he may be liable for his wife's debts. The bishop, who is writing a book on the history of marriage, suggests that Edith and Cecil should revive the Roman concept of marriage by contract, but he thinks a traditional marriage is better. The Bishop's chaplain, a lawyer, tries to draw up a contract, though it proves a difficult task. All the characters have ideas about what should be in the contract, based on their own experience. There is disagreement on medical, religious, financial and other matters.
Eventually they give up, agreeing that a standard marriage is easier, at least with the possibility of divorce. Cecil and Edith leave together and return married - though the ceremony involved the Beadle giving away the bride. They have arranged with an insurance company a deal that will free Cecil of responsibility for any future debt incurred by his wife. In return Cecil has provided a document declaring that if he commits a crime while insane, his wife may divorce him. Hotchkiss, who, it turns out was being pursued by Leo rather against his own wishes, falls in love with the siren-like Mrs George Collins. Leo therefore tells her ex-husband that their divorce must be revoked.

Question: What is the Bishop in the process of writing about?
Answer: The history of marriage
Alternative answer: the history of marriage