Some sequels seem fitting or inevitable while others, usually ones written by somebody besides the original and dead author, feel more like grave robberies. But the impulse toward exhumation can be hard to resist.
Novelists send their characters abroad for the same reason we send ourselves: for a change of pace, to get out of a rut, to shake off the rust. Henry James built a whole career on exploring the theme of Americans traveling abroad and being transformed by the experience.
When you're writing a book based on archival research and you have two children who come home from school at three, no matter how much you love libraries, you become grateful for Google. For three years, I sat down most mornings at my dining room table in my slippers and read newspapers in the 1870s. No need to travel to distant archives, or spend fruitless hours turning the wrong pages. I could open a browser, punch in a range of dates and a few search terms, and within seconds have a presorted queue of articles, every one of which was relevant.