Behind closed doors, with a unanimous vote, Beijing passed a secret law and imposed its writ on Hong Kong.
Its contents were only made public at the very moment the national security law came into effect, at 11pm Hong Kong time on Tuesday. It meets its critics most pessimistic predictions.
The four offences - subversion, secession, terrorism and collusion with foreign forces - all carry a potential life sentence .
The 66 articles of the law contain some extraordinary details. Damaging public transport can be classed as terrorism, for instance.
Beijing will set up a national security committee in Hong Kong whose work will be secret and whose decisions will not be subject to judicial review.
And acts performed by central government officials in relation to national security will not be subject to Hong Kong's jurisdiction.
The Hong Kong chief executive will personally be able to designate judges to handle national security cases.
If a judge makes a statement "endangering national security", they will be removed. Trials can be held without jury.
National security education, as defined by Beijing, will be taught to Hong Kong children.
There is a lot of text to pick through but the devil is not in the detail - the devil is in the ambiguity.
Offences are defined sweepingly. "Triggering hatred" towards the Hong Kong or Chinese governments is a crime.
"Interfering in, disrupting, or undermining" government activities is a crime.
Ultimately, what Beijing says goes.
The interpretation of the law is ultimately decided not by Hong Kong, but by the Standing Committee of the National People's Congress on the mainland.
Beijing has promised that Hong Kong's autonomy will nonetheless be protected and this is ostensibly spelt out in the new law: "The rights and freedoms, including the freedoms of speech, of the press, of publication, of association, of assembly, of procession and of demonstration shall be protected."
But only up to a point. Another provision, Article 62, states that the national security law trumps Hong Kong's existing law when they come into conflict.
Rights will exist only if Beijing decides they are not a matter of national security.
And Beijing tends to see any sort of speech as a matter of national security - look at the number of activists, lawyers and journalists sent to mainland jails.
This is the most significant change to Hong Kong in the 23 years since its handover from the UK. It is impossible now to say exactly what its consequences will be for the city.
But it certainly tells us something about the Chinese government now.
In years past, as it enjoyed its stratospheric economic rise, China was happy to at least pay lip service to international opinion and international commitments, including the Sino-British declaration of 1984, in which the Chinese Communist Party promised to preserve Hong Kong's autonomy until 2047.
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It no longer cares to wait that long, nor does it care much what the world thinks.
That may be because it thinks other countries are distracted by COVID-19, and must seize this moment.
But it is increasingly Beijing's general disposition, and it does not bode well.
The people of Hong Kong are the first to feel its effects.