Corporal Flack was a young Marution scout for General Darien. He was with Darien and company when they were trapped by King Lawrence and General Liddell at the Valley of the Rocks. Darien, Colonel Oliver, and several others were resting in a cave when General Liddell yelled for Darien to come out because the king wanted to kill him. Corporal Flack, who was outside the cave, confirmed to Darien that he was indeed trapped by signaling to Colonel Oliver that the king’s army was situated in four places on the ridge directly above the cave. Darien was ready to go out and surrender himself to the king, so that his men would not die. But before he could, the Corporal started running towards them and told them that a messenger had come up to the army and told them something, and then suddenly the King, General Liddell, and the whole army left faster than anyone thought possible.
In the book, Colonel Oliver was not with Darien when the King’s ambush occurred. He was with one of the other groups of Darien’s men, as the regiment had been split up into four groups. The Colonel saw the king leave and then came and told Darien what happened.
There was a scout who signaled Darien in the book about the King's army above the cave, but the scout’s name was not revealed. Also the scout was shot by one of General Liddell’s men as a demonstration of how effectively Darien was trapped.