Ben Bova & Myron R. Lewis 
Dueling Machine [PDF ebook] 

At first, the dueling machine seemed like a benign or even a helpful invention, allowing people to blow off steam and solve conflicts in a virtual reality-like environment. But before long, an evil tyrant discovers a way to use the device to inflict real and lasting harm on participants. Will the intrepid scientist who invented the technology be able to stop him before it’s too late?