Overdoses linked to fentanyl, a synthetic opioid up to 50 times stronger than heroin, killed nearly 30,000 people in the United States in 2017. Authorities say most fentanyl sold in the state of Pennsylvania can be traced back to China. We went to Kensington, an area considered a “ground zero” of America’s opioid crisis, in the Pennsylvanian city of Philadelphia, to find out how a drug funneled through from China is fueling a health crisis half a world away.