Gravity. The Alex Cave Series book 4.

They create a huge spiral tunnel down into a dormant volcano, and Geophysics instructor Alex Cave and his friend O'Conna descend deep into the mountain to discover the cause. What they find is more powerful than a nuclear weapon.

Janice Sloan, a ruthless woman dealing in stolen technology, manages to steal the device and takes it into the Nevada desert, but she has no idea what she's doing, and when she turns it on, birds start slamming into the ground around her.

She can't turn it off and abandons the device, and it begins dragging satellites from space and threatens to bring down the International Space Station. When it changes the orbit of the moon, the extreme tidal affect begins destroying shorelines on a global scale. Alex and his team think they can fix the problem, but they need to find the device to do it, and Sloan holds it for ransom.

The adventure doesn't end when a huge gold asteroid is on a collision course with Earth, and will impact in six days. His only chance of changing its trajectory is with the device, and he is running out of time to find it.

A fantastic ride, with thrilling scenarios, exhilarating situations, and nail-biting suspense, by this bestselling and award-winning author. How does he save civilization from extinction?