Prometheus Project: Bk. 3 Stranded

A fantastic alien city buried deep underground. What wonders - and what dangers - is it hiding? Ryan and Regan Resnick are the two youngest members of the Prometheus Project, a top secret team exploring a vast, abandoned alien city. But when they journey through a portal to a primitive alien planet, what begins as an ordinary day will quickly become a non-stop fight for their lives. Soon they are stranded on the distant planet, surrounded by vicious predators, and in the path of a raging river of lava. But surviving on the deadly planet might be the easy part. Because if they can get back to Earth, they will have to face a ruthless adversary who controls a mysterious alien device. A device that is the most powerful, dangerous, and unstoppable weapon the world has ever known...