DEREK STRANGE GOT down in a three-point stance. He breathed evenly, as his father had instructed him to do, and took in the pleasant smell of April. Magnolias, dogwoods, and cherry trees were in bloom around the city. The scent of their flowers, and the heavy fragrance of a nearby lilac bush growing against a residential fence, filled the air.

“You keep your back straight,” said Derek, “like you’re gonna set a dinner up on it. You ain’t want your butt up in the air, either. That way you’re ready. You just blow right out, like, and hit the holes. Bust on through.”

Derek and his Saturday companion, Billy Georgelakos, were in an alley that ran behind the Three-Star Diner on a single-number block of Kennedy Street, at the eastern edge of Northwest D.C. Both were twelve years old.