The safety of the pet steamer depended upon the skill and judgment of a mere boy, though everybody on board had entire confidence in him.

But the supreme moment came soon enough.
[Illustration: "Christy sprang to the Gun."-- Page 119.] A hardly perceptible light at the point he was so closely watching, first attracted the attention of Christy,--perhaps the lighting of the steward's match.

An instant later, the fireworks blazed up, and lighted up the smooth surface of the sleeping river.

No doubt the conspirators, who had chosen darkness because their deeds were evil, were astounded to see so much light suddenly thrown upon their enterprise.
Christy sprang to the gun, took a hasty sight, which satisfied him that the position of the gun had not changed a particle.

As the dark outline of the Vampire passed in range of the selected tree, the midshipman sprang down from the gun-carriage.
"Fire!" shouted he, in a determined though not very loud tone.
It was a tremendous explosion, and the echoes rolled out from the hills as though they were armed with heavy guns, and were taking part in the conflict.