“And now, Señor Falconer,” said the chief of police at last, “the best line of action for you is to return and keep a secret and strict watch. You know all I have told you, and what are my suspicions. It is fortunate, very fortunate, that your young lady friend has detected what is in progress. On my part I will send by to-night’s mail a report to the police of Madrid, who will be on the alert for any developments. They will place our great pathologist, Professor Barrera, at your disposal, should any analysis be required. We are at the moment quite powerless to act, but we look to you for such information as shall save the lady’s life.”
About noon on the following day Falconer called at the Mapleton’s house in El Pardo as though upon a casual visit. As soon as he met Sylvia, the girl called him aside, and whispered:
“I’m so glad you are here, Geoffrey. Mrs. Mapleton had another attack last night, but is better now. She is in the habit of eating but very little dinner, and taking some patent invalid food just before going to bed. I managed to save a little of it before Martin cleared it away. I’ve got it in a bottle upstairs.”
“Excellent. I will take it at once to Professor Barrera,” replied Falconer. “He will analyse it, and see whether it has been doctored.”
The young Englishman remained to luncheon, and then, without telling anyone of his journey to San Sebastian, he went back to Madrid, and there saw the Professor, who had already been warned by the police.
Next day, when Falconer called upon Professor Barrera, he was told that into the invalid food had been introduced the juice of a certain poisonous mushroom which produced the exact symptoms of acute indigestion, and which, when absorbed by the human body, was almost impossible to detect. It was one of the most subtle and dangerous poisons known to modern toxicologists.
“The mushroom is a large dark-grey fungus with scarlet spots and grows on the mountains. It is found often in the Guadarrama,” he said. “Whoever is using it must be an expert poisoner.”
With that knowledge, and the other knowledge he now possessed, Falconer waited until evening, and then returned to El Pardo, where he was asked to remain to dinner, and to sleep, as a motor excursion had been arranged for the following day.