“The cards must be marked!” was the thought that again flashed through Frank Merriwell’s mind.

But if they were marked and it was impossible to detect the fact, there was no way of exposing the crooked player. If they were marked, however, Merry believed there must be some way of detecting it.

Frank kept very still. Slipping his hand into an inner pocket, he brought forth something he had purchased that very afternoon, after talking with Morton concerning Darleton’s success at poker and his methods. Quietly he adjusted his purchase to the bridge of his nose.

He had bought a pair of smoked glass goggles!

The cards were being shuffled. The goggles changed the aspect of the room, causing everything to look dim and dusky.

The man who was dealing tossed the cards round to the different players. As this was being done, Frank detected something hitherto unseen upon the cards.

On the backs of many of them were strange luminous designs, crosses, spots, circles, and straight lines. These marks could be distinctly seen with the aid of the smoked glasses.

Lifting his hand, Merry raised the glasses.

The glowing marks vanished! A feeling of satisfaction shot through the discoverer.

“I have him!” he mentally exclaimed. “I have detected his clever little trick!”

It happened that Darleton received a pair of jacks and a pair of sixes on the deal.

One of the players “stayed” and Darleton “came up.”

On the draw Darleton caught another six spot, giving him a full hand.

He seemed to be looking at his cards intently, but Frank observed that he had watched every card as it was dealt.

In the betting that followed Darleton pressed it every time. At the call he displayed the winning hand.

But just as he reached to pull in the chips his wrist was clutched by a grip of iron.

Frank Merriwell had grasped and checked him.

“Gentlemen,” cried Merry, “you are playing with a crook! You are being cheated!”

Instantly there was a great stir in the room. Men sprang up from their chairs.

Darleton uttered an exclamation of fury.

“What do you mean, you duffer?” he snarled. “Let go!”

Instead of obeying, Merry pinned him fast in his chair, so he could not move.

“Yes, what do you mean?” shouted one of Darleton’s friends, leaping from another table and endeavoring to reach Frank. “Let go, or I’ll——”

Hugh Morton grappled with the fellow.

“I wouldn’t do anything if I were you,” he said. “Take it easy, Higgins. We’ll find out what he means in a minute.”

“Find out!” roared Higgins. “You bet! He’ll get all that’s coming to him for this!”

“Explain yourself, Mr. Merriwell,” urged one of the players. “This is a very grave charge. If you cannot substantiate it——”

“I can, sir.”

“Do so at once.”

“These cards are marked.”

“It’s a lie!” raged Darleton.

“You must prove that the cards are marked, Mr. Merriwell,” said another player. “They were but lately unsealed, and it seems impossible.”

“They have been marked since they were opened.”

“How?”

“With the aid of luminous marking fluid of some sort, carried in this man’s pocket. I have watched him marking them.”

“Liar!” came from the fellow accused; but he choked over the word, and he was white to the lips, for he had discovered that Merry was wearing smoked goggles, like his own.

“Let me get at him!” panted Darleton’s friend; but Morton continued, with the assistance of another man, to hold the fellow in check.

“Under ordinary conditions,” said Frank coolly, “the marking cannot be detected. Mr. Darleton has pretended it was necessary for him to wear dark-colored goggles in order to protect his eyes from the lights. Why didn’t he play in the daytime? Because he would then have no excuse for using the goggles, which he does not wear as a rule. With the aid of the goggles he is able to see and understand the marking on the backs of the cards. This makes it possible for him to tell what every man round the table holds. No wonder he knows when to bet and when to drop his cards!”

“It’s false!” muttered the accused weakly.

“If any one doubts that I speak the truth,” said Merry, “let him feel in Mr. Darleton’s coat pocket on the right-hand side.”

A man did so at once, bringing forth a little, tin box, minus the lid, which contained a yellowish, paste-like substance.

“That is the luminous paint,” said Frank.

“Further doubts will be settled by taking my goggles, with which I detected the fraud, and examining the backs of the cards.”

He handed the goggles over, releasing his hold on Darleton, who seemed for the moment incapable of action.

The excited players tried the goggles and examined the cards, one after another. All saw the marks distinctly with the aid of the smoke-colored glasses. They discovered that the four aces were marked, each card with a single dot, the kings bore two dots, the queens three dots and the jacks four dots. The ten spot was indicated by a cross, the nine spot showed two crosses, the eight a straight line, the seven two parallel lines, the six a circle, and there the marking stopped. Evidently Darleton had not found time to finish his work on the remainder of the pack.

And now Darleton found himself regarded with intense indignation and disgust by all save the fellow who had attempted to come to his aid. Indeed, the indignation of the men was such that they threatened personal violence to the exposed rascal.

It seemed that the fellow would not escape from the room without being handled roughly. Before the outburst of indignation, his bravado and nerve wilted, and he became very humble and apprehensive.

No wonder he was alarmed for his own safety. Several of those present had lost heavily to him, and they demanded satisfaction of some sort.

“He has skinned me out of hundreds!” snarled one man. “I’ll take it out of his hide! I’ll break every bone in his dishonest body!”

Two men placed themselves before the infuriated one and tried to reason with him.

“What are you going to do?” he shouted. “Are you going to let him off without doing anything?”

“We’ll make him fork over what he has won to-night.”

“Little satisfaction that will be!”

“We’ll find how much money he has on his person and make him give that up.”