"Why does he do it, Daddy?" asked Vi.

"Why does he do what?" returned her father, who was too excited and anxious to wish to be bothered by Vi's questions.

"Mun Bun. Why does he?"

"Don't bother me now," said her father. "It is bad enough to have Mun Bun disappear in this mysterious way——"

"But why does he disappear—and everything?" Vi wanted to know. "He's the littlest of all of us Bunkers, but he makes the most trouble. Why does he?"

"I'm sure," said Mother Bunker, who had overheard Vi, "you may be right. But I can't answer your question and neither can daddy. Now, don't bother us, Vi. If you can't find your little brother, let us look for him."

The whole party at the Oxbow Bend was roused by this time, and men, women and children were looking for the little lost boy. Some of the cowboys who were working with the moving picture people scurried all around the neighborhood on pony back; but they could see nothing of Mun Bun.

Russ and Rose had searched everywhere they could think of. Mun Bun had not been in their care at the time he was lost, and for that fact Russ and Rose were very thankful. This only relieved them of personal responsibility, however; the older brother and sister were very much troubled about Mun Bun's absence.

The smallest Bunker really had succeeded in getting everybody at Oxbow Bend very much stirred up. Even the usually stolid Indians went about seeking the little white boy. And Mun Bun was nearer the Indians just then than he was to anybody else!

The little fellow had gone wandering off after breakfast while almost everybody else was down at the fort listening to Mr. Habback's final instructions about the big scene that was to be shot. Mun Bun had already expressed himself as disapproving of the picture. He knew he would not look nice in it.

He came to the Indian encampment, and the only person about was an old squaw who was doing something at the cooking fire. She gave Mun Bun no attention, and he looked only once at her. She did not interest the little boy at all.

But there was something here he was curious about. He had seen it before, and he wanted to see in it—to learn what the Indians kept in it. It was a big box, bigger than Mother Bunker's biggest trunk, and now the lid was propped up.

Mun Bun did not ask the old woman if he could look in it. Maybe he did not think to ask. At any rate, there was a pile of blankets beside the box and he climbed upon them and then stood up and looked down into the big box.

It was half filled with a multitude of things—beaded clothing, gaily colored blankets, feather headdresses, and other articles of Indian apparel. And although there was so much packed in the box, there was still plenty of room.

"It would make a nice cubby-house to play in," thought Mun Bun. "I wonder what that is."

"That" was something that glittered down in one corner. Mun Bun stooped over the edge of the box and tried to reach the glittering object. At first he did not succeed; then he reached farther—and he got it! But in doing this he slipped right over the edge of the box and dived headfirst into it.

Mun Bun cried out; but that cry was involuntary. Then he remembered that he was where he had no business to be, and he kept very still. He even lost interest in the thing he had tried to reach and which had caused his downfall.

Of a sudden he heard talking outside. It was talking that Mun Bun could not understand. He was always alarmed when he heard the Indians speaking their own tongue, for he did not know what they said. So Mun Bun kept very still, crouching down there in the box. He would not try to get out until these people he heard went away.

Just then, and before Mun Bun could change his mind if he wanted to, somebody came along and slammed down the lid of that box!

Poor little Mun Bun was much frightened then. At first he did not cry out or try to make himself heard. But he heard the person outside lock the box and then go away. After that he heard nothing at all for a long time.

Perhaps Mun Bun sobbed himself to sleep. At least, it seemed to him when he next aroused that he had been in the box a long, long time. He knew he was hungry, and being hungry is not at all a pleasant experience.

Meanwhile the search for the smallest Bunker was carried on all about the Oxbow Bend. In the brush and along the river's edge where the cottonwoods stood, and in every little coulee, or hollow, back of the camps.

"I don't see," complained Rose, "why we Bunkers have to be losing things all the time. There was my wrist-watch and Laddie's pin. Next came Vi and Laddie. Then Mun Bun was lost in the tumble-weed. Then I got lost myself. Now it's Mun Bun again. Somehow, Russ, it does seem as though we must be awful careless."

"You speak for yourself, Rose Bunker!" returned her brother quite sharply. "I know I wasn't careless about Mun Bun. I didn't even know he needed watching—not when daddy and mother were around."

Nobody seemed more disturbed over Mun Bun's disappearance than Cowboy Jack. The ranchman had set everybody about the place to work hunting for the little boy, and privately he had begun to offer a reward for the discovery of the lost one.

To Cowboy Jack came one of the older Indian men. He was not a modern, up-to-date Indian, like Chief Black Bear. He still tied his hair in a scalp-lock, and if he was not actually a "blanket Indian" (that is, one of the old kind that wore blankets instead of regular shirts and jackets), this Indian was one that had not been to school. Russ and Rose were standing with Cowboy Jack when the old Indian came to the ranchman.

"Wuh! Heap trouble in camp," said the old Indian in his deep voice.

"And there's going to be more trouble if we don't find that little fellow pretty soon," declared the ranchman vigorously.

"Bad spirits here. Bad medicine," grunted the old Indian.

"What's that? You mean to say one of those bootleggers that sell you reds bad whisky is around?"

"No. No firewater. Heap worse," said the Indian.

"Can't be anything worse than whisky," declared Cowboy Jack emphatically.

"Bad spirits," said the Indian stubbornly. "In box. Make knocking. White chief come see—come hear."

He called Cowboy Jack a "chief" because the white man owned the big ranch. Rose and Russ listened very earnestly to what the Indian said, and they urged Cowboy Jack to go to the Indian encampment and see what it meant.

"What's a spirit, Russ?" asked his sister.

"Alcohol," declared Russ, proud of his knowledge. "But I don't see how alcohol could knock on a box. It's a liquid—like water, you know."

They trotted after Cowboy Jack and the old Indian and came to the big box that had been locked in preparation for shipping back to the reservation when the Indians got through their job here with the picture company. It looked to be a perfectly innocent box, and at first the children and Cowboy Jack heard nothing remarkable from within it.

"I reckon you were hearing things in your mind, old fellow," said the ranchman to the Indian.

The latter grunted suddenly and pointed to the box. There was a sound that seemed to come from inside. Something made a rat, tat, tat on the cover of the box.

"Goodness me!" murmured Rose, quite startled.

"That's a real knocking," admitted Russ.

Cowboy Jack sprang forward and tried to open the box.

"Hey!" he exclaimed. "It's locked. Where's the key? When did you lock this box?"

"Black Bear—him lock it. Got key," said the old Indian, keeping well away from the box.

"You go and get that key in a hurry. Somebody is in that box, sure as you live!" cried the ranchman.

"I know! I know!" shouted Russ excitedly. "It's Mun Bun! They have locked him in that box!"

"Oh, poor little Mun Bun!" wailed Rose. "Do—do you suppose the Indians were trying to steal him?"

"Of course not," returned Russ disdainfully. "Mr. Black Bear wouldn't steal anybody. He just didn't know Mun Bun was in there. I guess Mun Bun crawled in by himself."

Then he went close to the big box and shouted Mun Bun's name, and they all heard the little boy reply—but his voice came to them very faintly.

"We'd better get him out in a hurry," said Cowboy Jack anxiously. "The little fellow might easily smother inside that box."