The motorboat raced on down the bay. The storm clouds that had been collecting all morning now hung heavily in the sky. The bay was sullen and slate-colored, and a heavy sea was running. White caps broke on the surface of the water.
"Looks like a storm," Frank muttered. "Perhaps it's just as well we didn't turn back."
A streak of lightning split the sky; it was followed by a distant rumble of thunder. The Sleuth was riding the waves well, but there was a rocking motion that could not be avoided. The boat swayed from side to side as it plunged on.
After about five minutes Frank glanced behind.
The stranger was no longer standing up; he was sitting back against the cushions again and he still held the revolver levelled at the Hardy boys, but there was a curious expression on his face, an expression of nausea; his eyes were staring and his face was pallid.
For a moment Frank could not understand what the matter was. Then, as the boat gave a lurch more violent than usual, he understood.
He nudged his brother.
"Getting seasick!" he whispered.
Joe glanced back, and when he saw that the stranger's florid face had changed in hue from a deep red to a greenish white he knew that the motion of the boat was indeed taking its effect. He forebore an impulse to chuckle at their passenger's plight.
"Give her a little more gas," ordered the stranger, in a curiously feeble voice. "You're not going fast enough."