Following the defeat of Mauron during the Hundred Years' War, the Bretons, led by Bertrand Du Guesclin, took their revenge. In 1354, Calveley was captain of the English-held fortress of Bécherel. He planned a raid on the castle of Montmuran on 10 April, to capture Arnoul d'Audrehem, Marshal of France, who was a guest of the lady of Tinteniac. Bertrand du Guesclin, in one of the early highlights of his career, anticipated the attack, posting archers as sentries. When the sentries raised the alarm at Calveley's approach, du Guesclin and d'Audrehem hurried to intercept. In the ensuing fight, Calveley was unhorsed by a knight named Enguerrand d'Hesdin, captured, and later ransomed.