In 2019, Hong Kong's social stability and national security were put to a test by the outbreak of the legislative amendment controversy. The National Security Law was passed by the National People's Congress to stop the violence and restrain the chaos. It dealt a fatal blow to the anti-China forces that tried to promote Hong Kong independence and colluded with foreign forces to endanger national security. This will restore a calm and peaceful social order in Hong Kong. The enactment and implementation of the National Security Law is a major milestone in the practice of "one country, two systems", and is the anchor for the prosperity and stability of Hong Kong. This film reviews the causes and consequences of this law, as well as the process and effects of its implementation, with a view to raising the sufficient alarm, so that the whole society will adhere to the red line of national security and will not waver.