"I wish your mind hadn't been so slippery," remarked the engineer. "If you could only have had presence of mind enough to have brought an olive or two." "I tell you, Chief," said Jim, airily, "I'll have the dinner ready by the time you get your dress suit. But coming down to the plain English of it, I'm starved. Think of the exercise we have had since leaving the restaurant to join our friend on the sidewalk." "A man who would put you to all that trouble to speak to him is no gentleman," declared John Berwick whimsically. "He deserves to be hung," said Jim savagely; "anyone who would impose on a trustful nature like yours and make you run over twenty miles of landscape! But cheer up, John, I have a hunch that we will strike a pay streak of grub yet. Let's take one more scout around that mysterious castle yonder and then we will make a bee line for the nearest lunch counter." "Any time you give the word." "Well, I suppose that 'all's quiet along the Potomac,' so let's move." "Agreed, James," said the engineer. Then the two friends slipped through the soft darkness of the night and fog until they reached the iron rampart of the fence and went past the great gates. There was a gilt monogram on either side and in the center, but these things did not interest them. Then they went on to the south part of the grounds. "See that, John!" said Jim in a low voice. "A light in the tower," replied his friend; "now it's gone out again." They stood watching with breathless interest. There are lights and lights. Some are the mere commonplace of domestic peace set on a round table in a cozy room with children intent on the Frontier Boys. Then there is the weird light of a lantern moving unevenly across a field, or revolving along a hidden lane, and there is something of the dramatic in its yellow flame. Finally there is the light that shines under strange circumstances or peculiar surroundings that has a mystery of its own, a beacon of danger, or of sudden death. "It is again on this side, only higher up," announced Jim; "somebody going up those stairs, that's what it is." In a few moments the powerful lamp illuminated an upper room and they saw the interior distinctly. But what fastened their attention was the sight of a head that showed just above the sill of the windows. It must be the head of a child to reach no higher. But what would a child be doing up in that lonely tower. Jim gripped his companion's arm. "It's that infernal Mexican, Berwick!" he whispered. "No other!" said his friend. "And that light is a signal." "Can't be seen far even if the fog is thinner," objected Jim. "Broome is close in," said the engineer decisively. "It may be to serve as a guide for some party coming over the lonely moor," said Jim with much shrewdness. "Go to the head of the class, James," remarked Berwick; "that's a sound guess for a fact."