Joe Haldeman returns with a story about the horrors of war -- and how we might move past them. Julian Class is a physicist working on the largest particle accelerator ever built, a nanobot-constructed ring in the orbit of Jupiter. He is also a 'mechanic', someone who pilots the robotic combat mechs used by the US Army to fight a protracted war against a South America-Africa alliance. When he learns about the potential outcome of the Jupiter Project, he is forced to take action.