Sarah H. Bradford 
Harriet Tubman, the Moses of Her People [EPUB ebook] 

After reaching Philadelphia, Tubman began thinking of her family. 'I was a stranger in a strange land, ’ she said later. 'My father, my mother, my brothers, and sisters, and friends were in Maryland. But I was free, and they should be free.’

For 11 years Tubman returned again and again to the Eastern Shore of Maryland, rescuing some 70 slaves in 13 expeditions, including her three brothers, Henry, Ben, and Robert, their wives and some of their children. She also provided specific instructions for about 50 to 60 other fugitives who escaped to the north.