You have to make a few leaps of faith with this book and if you can do that you'll find an interesting story that harkens back to the 'good old days' of sf. English Professor Wil Stone and 3 of his academic friends have been getting together to play poker for quite some time. During one of these events, physics and astronomy teacher Derek Ironcraft presents what he believes to be a mystery to the group. He's got photos of the Sahara after a scan with ground penetrating radar which seem to show a stonehenge like portal. After being shown this, the group does what academics do best and take off to investigate.

(Source: Tor Books)