The summer of 1916 had come on like a furnace.

June had been blistering, the kind of month that drove city dwellers out of their brick apartments in Philadelphia and New York, down toward the promise of breezes off the Atlantic.

And so, they flocked eastward, to the sand, to the surf, to the small Shore towns of New Jersey strung like beads along the coast—Beach Haven, Spring Lake, Asbury Park, Matawan—soon swelling with life.

The ocean was the great relief. Cool, vast, and—so people thought—safe. To slip into its waters after days of choking city air was to feel reborn. The salt burned away the grime of coal smoke, the heat, the stress. Women waded in up to their knees, laughing nervously at the waves, while young men swam boldly out past the ropes, slicing through the water with broad strokes.

But beneath the glittering surface, the sea held its own dangerous secrets.