The codename "Shield" is the top-secret codename in the files of national security investigator Lin He, and it is also the identity he must hide from his family his whole life.
During a routine data screening, Lin He discovered that overseas intelligence networks were conducting extremely active penetration around a civilian quantum communication technology in this city. He was ordered to pretend to be the security director of the institute to investigate, but found that all the clues vaguely pointed to a sleeping information source that was internally marked as a "deep well". What made his spine even more chilling was that the key command to trace the "deep well" had a dangerous intersection with his path of tracking overseas spies deep in the database - which meant that a high-level mole codenamed "Mole" might be lurking in the intranet.
On one side is the deadly threat from overseas spies, and on the other side is the cold gun from within whose identity is a mystery. Lin He fell into unprecedented isolation, and every judgment may be irreversible. When he finally used the "shield" authority to access the core logs, the highest authority operation records he saw pointed to his most respected superior, who was also his fiancée's father.
The Shield's mission has never changed: to protect secrets until silence. But this time, is the ultimate bottom line he protects iron-clad discipline or the unquenchable fire of justice in his heart? Will the codename "Shield" eventually point to betrayal, or will it become the final sharp blade to pierce the darkness?
Mission: National Security Mission, Unsung Heroes