How did Amari get away from Clay?

After Amari and Polly escape from the storage room, they find Tidbit, and the three escape into the woods. They travel through the woods for two months and face many dangers of their way to Fort Mose, a place that provides sanctuary for runaway slaves. When Clay tracks them down, he begins to sexually assault Amari, describing all the things he will do to her..... what Clay doesn't know is that Polly is standing nearby with a musket. Polly shoots at Clay, but she only grazes him. The shock, however, gives the young women the opportunity to tie Clay up to a tree, which they do. They are not bothered again.