Six secret operatives are the military's top experts in covert ops and rescue missions. But this elite special force doesn't exist - at least not in the public eye. No one knows where they come from or to where they return. The group gathers for the most dangerous, most difficult, and most important missions and often operates in extreme conditions. They are known only by their code name: Invisible Six. The US military is under cyberattack. Computer failures have crippled every weapons system. Gizmo and Invisible Six must discover who is behind this attack and the culprits' aim. But the mysterious hackers seem one step ahead of I-6 at every turn, and their use of autonomous weapons keeps I-6 from getting close. Can Gizmo and I-6 stop the worst cyberattack in US military history? AGES: 10 to 11