Through the ingenuity and daring of his wife De Groot contrived to escape in 1621 by concealing himself in a trunk supposed to be filled with heavy tomes.
The trunk was conveyed by water to Rotterdam, from whence the prisoner managed to make his way safely to France.
Concurrently with the political trials the National Synod had been pursuing its labours at Dordrecht.

On November 13 rather more than one hundred delegates assembled under the presidency of Johannes Bogerman of Leeuwarden.

Fifty-eight of the delegates were preachers, professors and elders elected by the provincial synods, fifteen were commissioners appointed by the States-General, twenty-eight were members of foreign Reformed churches.

English and Scottish representatives took an active part in the proceedings.

The Synod decided to summon the Remonstrants to send a deputation to make their defence.