"Ah!" answered Sarrion, "that is an old trick. I have seen doors like that before. There are several in the Calle San Gregorio. Sitting on my balcony in the Casa Sarrion I have seen a man go into one house and look out of the window of the next a minute later."
"Mon has not arrived," said Marcos, with his eye on the road. "He has the carriage of One-eyed Pedro whose near horse has a circular shoe."
"But we must not wait for him. The risk would be too great. They may dispense with his presence."
"No," answered Marcos thoughtfully, looking at the smaller door which seemed to belong to the next house. "We must not wait."
As he spoke a carriage appeared at the farther end of the Calle de la Merced, which is a straight and narrow street.
"Here they come," he added, and drew his father into a doorway across the street.
It was indeed the carriage of the man known as One-eyed Pedro, a victim to the dust of Aragon, and the near horse left a circular mark with its hind foot on the road.
Evasio Mon descended from the carriage and paid the man, giving, it would seem, a liberal "propina," for the One-eyed Pedro expectorated on the coin before putting it into his pocket.
Mon tapped on the door with the stick he always carried. It was instantly opened to give him admittance, and closed as quickly behind him.
"Ah!" whispered Sarrion, with a smile on his keen face. "I have heard them knock like that on the doors in the Calle San Gregorio. It is simple and yet distinctive."