On through the water plunged the Sleuth, gaining slowly but surely on the craft ahead.
Once in a while Biff cast a hasty glance backward to wave mockingly at them. He misjudged an approaching wave on one of these occasions and the Envoy swerved; he lost valuable seconds righting the craft into its course again and the Sleuth gained.
The yacht was about a quarter of a mile distant when the Sleuth at last pulled up beside the other boat. Inch by inch it forged ahead until the bow of each boat was on a line with the other. Then the Sleuth's greater speed became manifest as it pulled away, leaving Biff shaking his head in exasperation.
Suddenly Joe, who had been looking at the passenger yacht in the distance, gave a shout of alarm.
"Look!" he cried.
Frank glanced up just in time to see an immense puff of black smoke bursting from above the deck of the yacht. Then, across the waves, was borne to their ears the roar of an explosion.
They could see figures running about on the deck of the boat. One of them, a woman, ran directly to the rail and began to clamber up on it.
"What on earth—" gasped Joe.
"She's going overboard!"
Another figure ran out, making a frantic grab at the woman who was balanced perilously on top of the rail. Then, her arms outspread, the woman jumped. The boys saw her plunge down the side of the yacht, and there was a splash as she hurtled into the water.