Joshua Ferris follows up his PEN/Hemingway Award—winning debut Then We Came to the End with The Unnamed, whose protagonist suffers from a mysterious disease that compels him to walk to exhaustion.

The Unnamed is a very sad book at points, yet it's also very funny. How do you think that one helps bring out the other?

It's always important to look for what might be funny in any given situation. When it's funny and also bleak, as it is in The Unnamed, it has a real edge to it and tends to come out as black humor. That's just the nature of the beast when you're writing a depressing book, but have a tendency to try to find the humor that might be there.

There are no tidy endings for the characters in this book. Tim and his wife Jane love each other throughout the novel, but Tim's disease keeps them apart. What are you playing with here?

At the end of the day, it is a book about family, about how this one particular family deals with this disease. The disease can be [anything] and a lot of people can actually find themselves familiar with the kind of questions that arise in the book. But the most important thing for me was that he was physically removed from the people that he loved. That brought up an enormous number of questions about what it means to actually be a family. Does constant presence in one another's lives make a family? How does separation affect one's love for a father or a husband? Those questions are particularly pertinent to a disease about walking.

There's a moment where Jane is looking through the mail, and she receives a letter from a doctor who is sure she knows what's wrong with Tim, but Jane just throws the letter away, since they've been through this before. Was this going to be the answer, which they'll now never know?

I think it should be read as a possible answer. I want it to be an intimation that an answer might exist. I want the reader to think that the answer could be on every next page. But when there's resistance to answering those questions, I think the story is actually able to work itself out in a more honest and compelling way, because that's how it works in life. It seems every day, we have a new advancement or a new discovery that might help people. We're always sort of grasping at hope. The answer is always right around the corner, and yet it eludes us. And that hope and despair are constantly trading places.