Fort Detroit
When Mary arrived at Fort Detroit, she was taken to an area where Indians were in line with their scalps and captives. When Mary arrived at the front of the line, she discovered the British were counting the number of scalps each brave produced and paying them.  
When the British paid for their Indian captive, Mary thought at first she was being ransomed. However, once the British began paying the Indians to capture the settlers, their wives and their children, they were so inundated with captives that by 1780 they could no longer feed and clothe them all. So although they paid for Mary's capture, they released her into the custody of her Indian captors.

Picture of British soldier (left) and settler (below) from the George Rogers Clark National Historical Park at Vincennes, Indiana.
Only the male settlers were kept; they were tried for treason and either put to death or kept as prisoners of war.
  Mary's Indian tribe remained at Fort Detroit for some time until venturing further into the Northwest Territory.
While at Fort Detroit, the Indians traded for some blankets, which unbeknownst to them, were infected with the small pox virus. The British, like the French before them, routinely provided the Indians with these blankets. That winter, Mary and her entire Indian tribe were stricken with the disease. Some, like Eagle Feathers, died. Mary survived and in the spring she attempted another escape...