Suddenly, our planet has a barrier around it. We learn through scientific means that time is passing much faster outside. We make Mars fertile (the barrier is selectively permeable) and plant a colony there. Just as Mars is beginning to get its own barrier, a Martian travels to the Earth.
Like any decent book, there's intrigue, deception, and surprises (some of which I didn't foresee, so very good surprises). It has a framing story which annoyed me until I got into it. I haven't read any other books published in 2005, so I can't say whether this should be nominated/voted for Hugo, but it's not the best of the books I've read in the last year. It's still a good book.