It has all come down to this. Stuck in an alternate universe while a resurrected Charlie wreaks havoc in their own, Arista and Frees are desperate to return home to stop him. Their only problem: they don't have a Quantum Gate. But their new allies are clever, and if they play their cards just right, they might find a way home after all. What they'll discover after being away for months is anyone's guess. It turns out things are worse than they ever could have imagined. Charlie, the psychotic AI run amok, has begun an all-out war against the remaining humans and autonomous machines, determined to wipe them from the face of the Earth. The only ones left to stop him are Arista and her friends. In order to defeat Charlie, they'll have to seek out the last original Artificial Intelligence, and there's no telling if he's even still alive.

If they fail, it could mean the end of both humanity and the machines…forever. CAUSALITY is the final chapter in the pulse-pounding QUANTUM GATE saga. Filled with unforgettable characters and a world in peril, this last installment will leave you guessing until the very end!