Two days after the attacks in Brussels, and two districts of the Belgian capital have become infamous—even among people who have never visited the city. Molenbeek and Schaerbeek, home to the alleged Paris attackers and the Brussels bombers, are quickly developing a reputation, perhaps exaggerated, as hotbeds of extremism. But what about a place called Forest? It was here, on March 15, that police almost caught Salah Abdeslam, a suspect in the Paris attacks, before he was eventually arrested five days later in Molenbeek. Not only was Forest home to Abdeslam, a man who allegedly bears some responsibility for the...