Mark Gridley's latest computer project - a program designed to protect online security by scanning for 'invisible' hackers - suddenly becomes very useful when his buddies, Dan Sanchez and Maj Green, are wrongly accused of accessing sensitive Net Force files and are suspended from the Net Force Explorers. It's crucial that Dan and Maj find a way to pierce the hacker's invisibility armour - but this hacker isn't afraid of killing to cover his tracks.