In retaliation, Sir Thomas Rempston invaded the duchy with a small army in January 1426, penetrating to the capital, Rennes,[1][2] before falling back to St. James-de-Beuvron on the Norman frontier.

The newly assembled Breton force first captured Pontorson, executing all the surviving English defenders and entirely destroying the wall after seizing the city.

At some point, men from Richemont's main force mistook for enemy relief a returning detachment, that had been previously tasked by the constable to survey the other side of the city, and panic ensued among the largely ill-trained Breton militia.

[7] The English defenders immediately decided to capitalize on this unexpected rout and came out of the city to inflict heavy losses on the fleeing Breton troops.

During the chaotic retreat, hundreds of men drowned crossing the nearby river while many others fell to the deadly bolts of the defenders' crossbows.

Any attempts Richemont may have made to rally them were unsuccessful and, in the night, they burned their tents and baggage and fell back in disorder to their point of departure near Fougres.