What is the main conflict in Restoration by Rose Tremain?

Restoration is a historical novel set in London, England during the 17th century, approximately 1660-70, during the reign of King of Britain Charles II. The principal character is Robert Merivel, who tells in the first person his coming of age story from age nine. He is a half-educated physician and surgeon. He leaves school when, following the death of his father, the King's glove maker, the King out of respect appoints Merivel as physician to the palace dogs. His status increases until the King orders him to marry the King's mistress Celia, as part of a scheme to hide her from the public eye as his mistress.