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."

He turned and illustrated the knock on the balustrade of the stairs up
which they had hastened.

"We will try it," he added grimly, "on that door when Evasio has had time
to go away from it."

They waited a few minutes, and then went out again into the Calle de la
Merced. It was the luncheon hour, and they had the street to themselves.
They stood for a moment in the doorway through which Mon had passed.

"Listen," said Marcos in a whisper.

It was the sound of an organ coming almost muffled from the back of the
empty house, and it seemed to travel through long corridors before
reaching them.

"They had," said Sarrion, "so far as I recollect, a large and beautiful
chapel in the patio opposite to that great door, which has probably been
built up on the inside."

Then he gave the peculiar knock on the door. At a gesture from Marcos he
stood back so that he who opened the door would need to open it wide and
almost come out into the street to see who had summoned him.

They heard the door opening, and the head that came round the door was
that of the tall and powerful friar who had come to the assistance of
Francisco de Mogente in the Calle San Gregorio. He drew back at once and
tried to close the door, but both father and son threw their weight
against it and slowly pressed him back, enabling Marcos at length to get
his shoulder in. Both men were somewhat smaller than the friar, but both
were quicker to see an advantage and take it.

In a moment the friar abandoned the attempt and ran down the long
corridor, into which the light filtered dimly through cobwebs. Marcos
gave chase while Sarrion stayed behind to close the door. At the corner
of the corridor the friar slipped, and, finding himself out-matched,
raised his voice to shout. But the cry was smothered by Marcos, who leapt
at him like a cat, and they rolled on the floor together.

The friar was heavier and stronger. He had led a simple and healthy life,
his muscles were toughened by his wanderings and the hardships of his
calling. At first Marcos was underneath, but as Sarrion hurried up he saw
his son come