“The main part of the church is all right, but they never use the other part. I don’t know whether it was partially destroyed in a war or whether it just caved in from old age.”

“How old do you think this church is?”

“I don’t know exactly, but it’s several hundred years old. I’ve heard that it’s one of the oldest buildings in this part of Mexico. All the better classes of people attend the large modern cathedral across the Plaza.”

“May we go over to the old church? I’d love to see it.”

“Why, yes, we’ll have time to go over there before lunch. There isn’t much to see, so it won’t take us long.”

Florence turned and said something in Spanish to Juana; then the three girls started out of the kitchen door. “Before we go,” Florence added, “I’ll show you this other room just across the hall—there’s nothing interesting or unusual about it, though. It has only one window looking out on the back street. There’s nothing but the back of that old church to be seen from it.”

After glancing about this room they hurried on down to the street, Jo Ann in the lead. She could scarcely wait to visit the old church.

As they started across the street, Peggy looked longingly toward the Plaza and the crowded streets of the business section of the city. She much preferred sightseeing in that direction, but she knew Jo Ann had set her heart on seeing the old church and that there was no changing her.

A few minutes later the girls passed under the old stone arch and into the vestibule with its font of holy water, then walked softly on into the church.

Having come in from the bright sunlight, they were unable at first to distinguish anything except the candles burning on the altar. A reverent silence lay over the entire building. With her finger to her lips Florence motioned Jo Ann and Peggy to a bench. They sat down quietly, careful lest they disturb the peacefulness of the place.

As their eyes became accustomed to the dim interior, they noticed several figures with black shawls about their heads and shoulders, kneeling at the altar. A woman with a baby in her arms and a tiny, half-naked tot beside her was kneeling before the statue of Mary, Mother of Jesus, her lips moving in silent prayer. Direst poverty was evident among all the worshipers.

Many minor details that had escaped Peggy’s eyes caught and held Jo Ann’s attention. The benches, altar rail, and pedestals, she noticed, were hand hewn and decorated with exquisite carving; the statues were different from any that she had ever seen; and even the candles were unusual—probably, hand dipped, she decided.

For almost an hour they sat there silent, Jo Ann intent in absorbing the atmosphere of this ancient building.

“I feel as if I’d actually stepped back through the centuries into the Mexico of ages past,” she thought dreamily.

By this time Peggy had begun to get restless. To her the place seemed close and stuffy, the odor and fumes of the candles suffocating. Without saying a word she rose and went outside. Leaning against the wall in the shadow of the stone arch, she waited for the girls and amused herself by gazing idly at the rear of Florence’s home across the street.

“Florence, I don’t like to make remarks about your house,” she said, half smiling as Florence and Jo Ann drew near, “but from the rear it looks more like a fort or a prison than a home.”

“It reminds me of an old castle with its high stone walls and heavy iron bars at the windows,” added Jo Ann, gazing over at the house.

Florence smiled good-naturedly. “It doesn’t look very homelike, I’ll admit. I don’t believe I’ve ever noticed it before from this viewpoint. I never come to this old church—at least, I haven’t been here for several years. As I said before, only people of the lowest classes attend this church.”

“I didn’t see a window in your hall,” Jo Ann suddenly remarked to Florence. “I thought I noticed a shaded light burning on that little table at the end of the hall.”

“There isn’t a window in the hall—it’s dark as pitch there, and we have to keep a light burning day and night.”

“Then how do you account for that little narrow, crosswise opening up there in the wall? There it is on a level with the top of the kitchen and back bedroom windows.”

“I don’t know.” Florence gazed puzzledly at the small opening. “I’ve never seen a window like that on the inside of the house, and I know I’ve seen every inch of the walls inside.”

“Well, there it is—a tiny window, just as plain as the nose on your face.”

In silent amazement Florence stared at this narrow opening high up in the bleak stone wall.

“That certainly is strange!” she said finally, her brows drawn together in a thoughtful frown.

“It certainly is,” agreed Jo Ann and Peggy, equally mystified.

Everything was forgotten now except this queer window. Why was it there? Into what did it open?

CHAPTER II
THE SEARCH BEGINS

“This is the strangest thing I’ve ever heard of,” declared Florence as they hurried back to the house, eager to examine the rear wall from the inside.

“How long have you lived here, Florence?” asked Jo Ann. “I’m sure I’d have seen that window long before this if I’d been in your place.”

“We’ve lived here about eight years, but, as I told you, I’ve only been in that church a few times, and I’ve never walked down that back street.”

“Lived here eight years and never walked back of your own house!” exclaimed Jo Ann in surprise. “Who ever heard of such a thing?”

“But you don’t understand,” Florence replied. “It isn’t exactly proper for me to wander down that back street.”

Both girls opened their eyes wide in astonishment.

“Not proper to go back of your own house!” ejaculated Peggy. “The very idea!”

“Yes, you see it’s only a narrow street leading to one of the poorest sections of the city. Only the very lowest class of people live on it. Mother and I drive down on the next street sometimes, accompanied by Felipe, to carry food and clothes to the destitute families, but I’ve never been down that narrow street.”

“It must be something like it is on the street cars at home,” Jo Ann said thoughtfully, coming to Florence’s assistance. “You know how they are, Peggy—one section marked ‘Colored,’ and you never sit there.”

Up the long flight of stairs they ran to the Blackwells’ apartment, each girl eager to be the first to solve the mystery. Jo Ann’s long legs carried her ahead of Florence and Peggy, who arrived a moment later out of breath.

There stood Jo Ann staring blankly at the solid plastered wall at the end of the hall.

“I’m sure this is where that window ought to be,” she said finally in a perplexed tone.

“There certainly isn’t any sign of one that I can see,” added Peggy, while Florence gazed silently at the spot where she thought the opening should be.

Just then Juana ran in from the kitchen to see what had caused so much commotion in the silent old house. “Florencita! Que es [What is it?]?” she asked in alarm.

“It’s nothing,” replied Florence in Spanish. Understanding the superstitious nature of the Indians, she thought it wiser not to tell Juana about this mysterious window for the present.

Juana stared in shocked surprise. Something was wrong, she was sure. Young ladies of the best