The Network is an organization in The Hardy Boys Casefiles book series.
The Network is a top-secret government agency in the same branch as the CIA and FBI, but even to most people in those organizations, The Network is unknown. After the events of Casefiles #6 The Crowning Terror and Ultra-Thriller #2 The Alien Factor, The Network took over control of everything that Espionage Resources (another top-secret government agency) ran, due to high corruption in that agency.
Frank and Joe Hardy (the Hardy boys of the title) first found out about The Network (in Dead on Target) when they met one of the agency’s best agents, the Gray Man. At the time the Hardys were investigating a car bombing that had killed Joe’s girlfriend, Iola Morton. The Gray Man offered to help find the person who planted the bomb, the Hardys accepted his offer and with his help Frank and Joe learned that it was not a person that planted the bomb, but The Network’s worst enemy - a worldwide group of terrorist group that calls themselves The Assassins. Since then the Hardys have worked with the Network on many cases.