Dr. Dilan Ellegala arrives in Tanzania, shocked to find the entire country has just three brain surgeons for its population of forty-two million. Haydom Lutheran Hospital lacks even the most basic surgical tools, not even a saw to open a patient's skull. Here, people with head injuries or brain tumors heal on their own or die. When confronted with a villager suffering from a severe head trauma, Dilan buys a tree saw from a farmer, sterilizes it, and then uses it to save the man's life.

Yet Dilan...