For 30 years, Area X has remained mysterious, remote, and concealed by the government as an environmental disaster zone - even though it is to all appearances pristine wilderness. Over the same period, a secret agency known as the Southern Reach has monitored it and sent in expeditions to try to discover the truth. Some have suffered terrible consequences. Others have reported nothing out of the ordinary. Now, as Area X seems to be changing and perhaps expanding, the next expedition will attempt to succeed where all others have failed. What is happening in Area X, and what is the true nature of the invisible border that surrounds it?