In August 1757, French forces under Montcalm and their native allies under the Assassin Kesegowaase besieged Fort William Henry. After days of bombardement, the British garrison under the command of George Monro surrendered on 9 August. Montcalm offered to let the British keep their arms and colors, an offer gladly accepted by Monro.
As Monro and his troops retreated the following morning however, Kesegowaase and the natives ambushed the force and broke the terms of the surrender in the process. Despite Montcalm's attempt to stop the massacre, Kesegowaase and his men were able to kill many of the British troops.
Throughout the war, Montcalm and his officers were served food by the father of Stephane Chapheau. In 1759, Montcalm was in charge of defending Quebec City from the British. After a three-month siege, the British forces under James Wolfe attacked from the Saint Lawrence River on 13 September. Rather than awaiting reinforcements, Montcalm chose to lead his men directly into battle at the Plains of Abraham. Both Chapheau and Montcalm died as a result.