According to Sara Lloyd, at thedigitalist.net:
"Just as we are poised to publish the the seventh novel in David Hewson’s beguilingly atmospheric and addictive Rome series, Dante’s Numbers, David has shrewdly agreed to an experiment to give away the first of his novels featuring the popular detective, Nic Costa, as an unDRM’d ebook.
You can download the ebook from Scribd "
Apparently it'll only be up until October 15th this year. I've never done more than glance at the Scribd site, and I haven't tried downloading the book yet, but it sounds interesting at the very least.