pretty definite, I shall be much tempted to take the next down-river boat and catch the Bolivia at Para. After all, I have some more responsible work in the world than to run about disproving the assertions of a lunatic. Now, Roxton, surely it is time."
"Time it is," said Lord John. "You can blow the whistle." He took up the envelope and cut it with his penknife. From it he drew a folded sheet of paper. This he carefully opened out and flattened on the table. It was a blank sheet. He turned it over. Again it was blank. We looked at each other in a bewildered silence, which was broken by a discordant burst of derisive laughter from Professor Summerlee.
"It is an open admission," he cried. "What more do you want? The fellow is a self-confessed humbug. We have only to return home and report him as the brazen imposter that he is."
"Invisible ink!" I suggested.
"I don't think!" said Lord Roxton, holding the paper to the light. "No, young fellah my lad, there is no use deceiving yourself. I'll go bail for it that nothing has ever been written upon this paper."
"May I come in?" boomed a voice from the veranda.
The shadow of a squat figure had stolen across the patch of sunlight. That voice! That monstrous breadth of shoulder! We sprang to our feet with a gasp of astonishment as Challenger, in a round, boyish straw-hat with a coloured ribbon—Challenger,
