In recent years, Hezbollah has stepped up its activities beyond Lebanon’s borders. This uptick has been clearest in the Middle East—in Iraq, Yemen, and especially Syria—but plots have also been thwarted in South America, Asia, Europe, and now, possibly, the United States. Reports of Hezbollah activity in North America are not new, though such reporting tends to focus on the group’s fundraising, money laundering, procurement, or other logistical activities from Vancouver to Miami. But last month, the criminal prosecution and conviction in New York of the Hezbollah operative Ali Kourani revealed disturbing new information about the extent of Hezbollah’s operations...