His fellows clustered about him. "What do you mean?" said Captain Hardy eagerly. "Explain."
"Well," said Willie, "when I followed that grocer's boy the other day, I saw him give the grocer a dollar which he said he had collected for sugar. The grocer put it in his pocket. But when I gave him money for candy he dropped it in his till. Just after I left the store and turned the corner a man drove up in a motor. I noticed him because he turned his car completely around and stopped at the curb. He got out and left his engine running. When I crossed the street to meet you, after you whistled, I dodged a motor-car. It was the same car, but I thought nothing of it." He paused, as though collecting his thoughts.
"Go on," said their leader eagerly.
"To-day," resumed Willie, "Roy followed that same grocer's boy from the house on the cliff to the grocery store and saw him give the grocer a dollar, which he said he had collected for sugar. The grocer dropped the coin in his pocket, but he put Roy's nickel in his drawer. A minute later an automobile driver came in. The grocer said he owed him a dollar and gave him the coin from his pocket. That driver was the same one I saw the other day."
"How do you know?" interrupted Captain Hardy. "You didn't see him to-day?"
"But Roy saw him. He's a tall man with black hair and with a scar on his left cheek. That's the man I saw, and it's the man who drove up to the house on the cliff the other day. I knew that I had seen him, but I couldn't remember just where." For a moment he stood silent, fairly panting with excitement.
"Well?" said Lew. "What about him? The grocer could owe him a dollar as well as anybody."
"But he didn't owe him a dollar," cried Willie. "Don't you see? The spy in the house below gave that dollar to the errand boy. He gave it to the grocer. He gave it to the motor driver. It's the same dollar. He didn't put it in the till with the other coins. He kept it in his pocket separate. That automobile driver is the man who carried the messages to the wireless. The messages are on the dollars."