Cross and the Switchblade, The
This classic book tells the incredible story of David Wilkerson's call to minister to urban street gangs in New York City in the 1960s. It was a best-seller for years after its release. Wilkerson's call eventually led to a world-wide ministry known as Teen Challenge. There's probably a chapter near you.
And if you're of a certain age, you surely remember the 1970 film version starring Pat Boone... and Erik Estrada in his first role!
This is the 45th Anniversary edition from 2008. Paperback.