As it appeared that the garrison were prepared to give battle outside the walls, the whole French army prepared to move against them.
In the meantime Sir Walter Manny, with 100 men-at-arms and 500 horse archers, issued by a sally-port on the other side of the town, and with all speed rode round to the rear of the French camp.

There he found none to oppose him save servants and camp-followers, and making his way straight to the tent of Charles of Blois, where the two knights were confined, he soon freed them from their bonds.

They were mounted without wasting a moment's time upon two spare horses, and turning again the whole party rode back towards Hennebon, and had reached the postern gate before the fugitives from the camp reached the French commanders and told them what had happened.
Seeing that he was now too late, because of De Clisson's sortie, Charles of Blois recalled his army from the attack, in which he could only have suffered heavily from the arrows of the archers and the missiles from the walls.

The same day, he learned from some prisoners captured in the sortie, of the undiminished spirit of the garrison, and that Hennebon was amply supplied with provisions brought by sea.

His own army was becoming straitened by the scarcity of supplies in the country round, he therefore determined at once to raise the siege, and to besiege some place where he would encounter less serious resistance.
Accordingly, next morning he drew off his army and marched to Carhaix.
Shortly afterwards the news came that the Earl of Northampton and Robert of Artois, with their force, had sailed, and Don Louis, with the Genoese and other Italian mercenaries, started to intercept them with a large fleet.