What is the plot related to Olivia and Ethan Miller in the novel?
Without reading the novel, it's hard to tell the exact plot involving Olivia and Ethan Miller. However, it's possible that they are part of a story set in a particular time period, say the 19th century. They could be involved in a social or political struggle of that time. For instance, if the novel is about the fight for women's rights, Olivia might be an active advocate while Ethan could be either supporting her or having his own conflicted views on the matter. Their interactions and the events that surround them would then form the plot of the novel.
The plot related to Olivia and Ethan Miller could be really diverse. Maybe they are trying to solve a mystery in the novel. It could be a mystery about a missing person, or an old family heirloom. They start investigating, and as they dig deeper, they find out things about themselves and their families that they never knew before. Their relationship could also be evolving during this process, from being strangers or acquaintances to becoming closer friends or even more than that.