The night before the battle:
Grouchy had decided that he now had to make a stand having already surrendered almost all the ground gained. Now reinforced by the Young Guard and the 7th Division he was determined that the allies would be repulsed before they step foot on French soil. With messengers arriving bringing news of Napoleon's victory over Blucher, additional pressure is on Grouchy to recover lost ground.
For the Prince of Orange, glory is beckoning. At long last he has a sizeable force thanks to the Prussian arrival that will enable him to push on to France.
As his troops make camp for the night, an exhausted messenger arrives at the Prussian commander, Ziethen's tent. A sealed envelope is passed to Ziethen containing a hastily scribbed note from Blucher. "Army routed by Napoleon at Ainsworth. Falling back to make a stand at Grissburg (capital). Make with all haste to my position. Prussia in mortal danger."
Ziethen is left with a horrendous decision to make. He knows that if he abandons The Prince of Orange now it will mean certain defeat for him the next day. After consulting with his Brigade commanders he decides that he will stay for one day only. He calculates that if the Dutch/Belgians lose badly it could clear the way for Grouchy to advance on Prussia. Therefore, they must defeat Grouchy the next day after which he will march to join Blucher.