"ET TU, Brute!" That Germany's Chancellor, Dr Helmut Kohl should plunge the disabling dagger into the treaty has shocked her allies profoundly. A last minute volte-face by Bonn on asylum and immigration policy has undone much of the advantage of treaty reform in justice and home affairs co-operation, diplomats here were saying last night.
Agreement on giving the EU institutions a new role in the area, and the incorporation of the Schengen Treaty on border controls into the EU, with opt-outs for Britain, Ireland and Denmark had been largely agreed before the German announcement. It provoked anger among the more integrationist countries.
The combination of opt-outs and the German insistence on majority voting means that decision-making in the area will, they believe, be more complex than it is. Yet the purpose of this summit was precisely the opposite.
Ireland's position on border controls, like Britain's, and their common travel area, are secured in protocols to the treaty - "what we asked for and what we got", British spokesman said, echoing similar Irish comments. The British Prime Minister, Mr Tony Blair, had made clear that the British right to control its borders would have to be copper-fastened in the treaty.
The protocol guarantees that Britain, uniquely, "shall be entitled to exercise at its frontiers with other member-states such controls on persons seeking to enter the United Kingdom as it may consider necessary". And the guarantee extends to Ireland as long as it maintains a common travel area with Britain.
But the Irish made clear they were distancing themselves from the British opt-out policy, with a special declaration attached to the treaty pledging to take part in the "flanking" measures associated with Schengen, like police co-operation "to the maximum possible extent". It also notes that Ireland's non-participation in the full Schengen arrangements is only due to its wish to preserve the common travel area with Britain.
The final version of the treaty also provides much simplified mechanisms for Irish or British opt-ins to those Schengen-associated policies or projects in which they want to participate. As a new project is developed they will simply have to decide to participate. If the project is underway, only a qualified majority vote can block their participation.
Following the German intervention, leaders reluctantly agreed that collective decisions on common immigration, visa and asylum rules and on the control of external frontiers must be unanimous. After five years there will be a vote again, it must be unanimous - on majority voting.
But the issues are brought from the so-called "Third Pillar" to the "First" - that is, from the realm of inter-governmental co-operation to decision-making involving the EU's institutions. The Commission gets the right to initiate proposals and the Parliament a right of oversight.
Other areas of justice and home affairs, mainly enhanced co-operation between police, customs, and judicial authorities, the strengthening of Europol, and the reinforcing of provisions on fundamental rights were agreed with little debate in a treaty section entitled, "An area of freedom security and justice".
