“Arthur Gentrie.”
“Junior? I thought you said he...”
“No, the father. He’s the one who went down in the cellar. He says he found the can lying in the box and opened it in order to mix up paint in it. Then he threw the top away, but you notice that when Steele became interested in the top, Gentrie saw that the tops were substituted. The one with the code message on it remained in the box, and one that had no message was put on the workbench.”
Della Street said, “My gosh, Chief, it’s perfectly obvious, now that you mention it. The way you sum it up, it sounds rather damning.”
Mason pulled the sheet of typewritten paper over to him, started studying it. Abruptly, he laughed.
“What is it?” she asked.
“That code,” he said. “It’s absolutely simple.”
“You mean you can read the message?” Della Street asked.
Mason nodded. “It’s absurdly simple when you approach the problem from the right angle.”
“What’s the right angle?”