The Cap leader, Ture Rudbeck, arrives at Stockholm on August 16 with news of the insurrection in the south, and Gustav finds himself isolated in the midst of enemies.

Sprengtporten lies weather-bound in Finland, Toll is five hundred miles away, and the Hat leaders are in hiding.

Gustav hereupon resolves to strike the decisive blow without waiting for Sprengtporten's arrival.
He acts promptly.

On the evening of  August 18, all the officers whom he thinks he can trust receive secret instructions to assemble in the great square facing the arsenal on the following morning.

At ten o'clock on August 19, Gustav mounts his horse and rides to the arsenal.

On the way, his adherents join him in little groups, as if by accident, so that by the time he reaches his destination he had about two hundred officers in his suite.

After parade he reconducts them to the guard-room in the north western wing of the palace, where the Guard of Honor has its headquarters, and unfolds his plans to them.

Gustav now dictates a new oath of allegiance, and everyone signs it without hesitation.

It absolves them from their allegiance to the estates, and binds them solely to obey "their lawful king, Gustav III".

Meanwhile, the Privy Council and its president, Rudbeck, have been arrested and the fleet secured.

Gustav makes a tour of the city and is everywhere received by enthusiastic crowds, who hail him as a deliverer.

On the evening of August 20, heralds roam the streets proclaiming that the estates are to meet at the palace on the following day; every deputy absenting himself will be regarded as the enemy of his country and his king.

On  August 21, the king appears in full regalia.

Taking his seat on the throne, he delivers his famous philippic, viewed as one of the masterpieces of Swedish oratory, in which he reproaches the estates for their unpatriotic venality and license in the past.

A new constitution, the Instrument of Government, is read to the estates and unanimously accepted by them.

The diet is now dissolved.