he rapped the table nervously, "I know
nothing about it."

"All right, all right; we're wise," Slim assured him confidently. "Don't
you worry. Come on, Joey. Got the money?"

"Have I? Oh, no; I'm goin' ter leave it right here," grinned Joey,
enjoying his own irony hugely.

Still chuckling, he arose and shuffled out, followed by the unsavory
Slim.

Outside, and on the road to the village, Slim began to be obsessed by
doubts.

"Some way, I don't jes' trust that Mortlake," he said. "You're sure that
bill is all right, Joey?"

"Sure? Well, you jes' bet I am. Here, look at it yourself. All right,
ain't it?"

He drew out the bill and handed it to Slim for his inspection.

"And the best of it is," he chuckled, while Slim inspected the bill
carefully, "the best of it is, that I wasn't conformin' to the exact truth
when I told Mortlake that we'd spent all the other coin. I've got the best
part of it left."

"Good," grunted Slim, turning the twenty-dollar-bill over and examining
the reverse side, "that being the case--hullo!"

"What's up?" asked Joey.

For reply Slim handed the bill to Joey, pointing with a grimy first finger
at something on the reverse side.

It was an "O," scrawled in dull red ink.

"That would be an easy bill to identify," commented Palmer, uneasily,
"wonder if this can be a trap?"

"Well, keep your suspicions to yourself for a while," counseled Joey; "we
don't need to break it till we make sure."

CHAPTER XII.

WHAT HAPPENED TO ROY.

It was the next evening. Mortlake, sitting at his desk, looked up as a
quick step sounded outside. The factory was in darkness as the men had
gone home. Only a twilight dimness illuminated the little glass sanctum of
the inventor and constructor of the Mortlake Aeroplane.

"Come in," said Mortlake, as the next instant a sharp, decisive knock
sounded.

Lieut. Bradbury, in a mufti suit of gray, stepped into the office.

"Ah, good evening, lieutenant," said Mortlake, rising clumsily to his feet
and offering a chair, "I was beginning to despair of you."

Bradbury, genuinely worried, lost no time in plunging into the object of
the interview.

"That message you sent me--what does it mean?" he asked. "I can scarcely
believe----"

"Nor could I, at first," said Mortlake, with assumed sorrow. "It cut me
pretty deep, I tell you, to think that a boy who was in negotiations with
his own government for a valuable implement of warfare, should deal with a