Master Lockton has money hidden in Madam Lockton's linen chest.
The money that Master Lockton has hidden in his wife's linen chest is money that he and the other conspirators plan to use in order to bribe Patriot soldiers. Lockton plans to offer members of the Patriot army money and the promise of land if those soldiers agree to fight for the British army.
Isabel learns about the money and the plan in chapter nine. She is about to enter the room where Lockton and his friends are meeting, and she overhears a comment about money. Isabel then peers through a crack in the door, and she sees Lockton pull out fistfuls of money from the linen chest. She then hears Lockton explain the specifics of the bribe and how the money will be distributed by two men working out of different taverns.
"Every man willing to switch sides is to be paid five guineas and two hundred acres of land. If he have a wife, an additional hundred acres. Each child of his blood garners another fifty."