THERE was a buzz of muffled conversation among the passengers, and before anyone could ask anything further, the captain had disappeared into the cabin.

“This is a fine howdy-do,” snorted Joe Lewis, peering out at the shoreline. “What do they take us for, a bunch of livestock?”

“Jove!” exclaimed one of the passengers, looking up through his large glasses. “The bally ship is a good half day’s journey from Mombasa.”

“It’s a horrible shame, that’s what it is,” came from Cecil Purl Stone, who also was at the rail. “Here I am in perfect readiness to look upon Mombasa, and this had to happen. I’m going straight to my suite.”

“Wonder how it all happened?” inquired Bob.

“That we don’t know, Son.” Mr. Holton’s temper was also being tried. “But now that it has happened, there’s no way out, only to wait.”

“I took for granted the Zanzibar’s navigators were competent,” said Mr. Lewis. “However, such things do happen occasionally.”

Although the naturalists and their sons were disappointed, there was nothing they could do but wait. Just how much longer it would be, however, they did not know.

To the vexation of all, the Zanzibar steamed for the remainder of that afternoon and evening without sighting the city of its destination. It was not until eight o’clock that night that Mombasa could be outlined in the distance, and then, of course, only the lights could be seen.

Bob and Joe, together with their fathers and many other passengers, stood at the prow of the ship, waiting for land to come up to meet them.

The broad beam of the vessel’s searchlight illuminated the water ahead perfectly. At last the Zanzibar was making directly for the harbor.

“Not much to be seen at night,” observed Joe. “But I guess we’ll be able to look around in the morning.”

They watched interestedly as the ship moved slowly into the harbor. Aside from a few small ships and native dhows, there was no water traffic in sight. Neither was the dock easily visible.

“Suppose we turn in, boys,” suggested Mr. Holton. “If we get to bed early, we can be up early. And the sooner we put ashore and make arrangements for our exploration venture, the sooner we can be on our way into the heart of Africa.”

The heart of Africa! Bob and Joe thrilled at mention of this. Often had they longed for such a venture into the Dark Continent, but not until now had that longing been satisfied.

The chums needed no urging to follow Mr. Holton’s suggestion to retire, for they desired to be up early the next morning.

“I don’t know whether I can sleep or not, though,” laughed Bob, as he and his friend walked to their stateroom. “I’m afraid I’ll be thinking too much about Africa. Think of it, Joe. We’re here—in Africa!”

“Not quite,” Joe reminded him. “We’re still on the Zanzibar, don’t forget.”

“Gosh! That’s right. I almost forgot.”

The boys slept soundly, but because they had set their “mental alarm clocks,” as Joe called it, they awoke before six in the morning.

But if they considered themselves “early-birds,” they were to throw away the title promptly when they caught sight of their fathers standing on deck with their baggage.

“How in the dickens did you manage to get up so early?” demanded Joe. “You must have got out of bed at four to have brought all that stuff out here.”

“We’ll have a big day before us, boys,” said Mr. Holton. “Let’s leave the ship at once.”

But before doing so the youths walked out to the rail to view their surroundings.

The sight that met their eyes made them gasp, so different was it from anything they had previously seen.

Before them was the new port, which contained numerous docks, warehouses, and the like. To one side they saw the old harbor with its numerous native ships and boats. Beyond the waterfront were the prominent buildings of the city, while not far away was the old Portuguese fort. Farther away was the bright green of endless tropical vegetation.

“So this is Africa,” muttered Bob. “What do you think of it?”

“Pleases me, all right,” grinned Joe. “I’m longing to get into the jungle.”

“Come along, boys.” It was Mr. Holton’s voice. “Gather up your baggage and come back on deck. Do it as rapidly as you can.”

During the next ten minutes the youths worked furiously, attending to such things that they had not already packed. On their way down the hall they stopped at Cecil Stone’s suite to have a parting word with that young man. But apparently he had left, for no one answered the knock.

“The last we’ll see of him, maybe,” remarked Bob, picking up the cases he had been carrying.

On deck, Bob and Joe found a large number of passengers amassed ready to move down the gangplank. There was an exchange of parting words, and the chums left with their fathers and made their way to a hotel, in which they had previously engaged rooms.

“What’s next?” inquired Joe, after they had had breakfast.

“Ben and I want to look up an old friend,” said Mr. Holton. “A Mr. George Seabury. He used to be a mighty hunter.”

“Used to be?” queried Bob. “What do you mean, Dad? Is he old or something?”

“What I meant, Bob, is that several years ago he was charged by a rhino and has not had full use of his legs since. He can walk, but doesn’t do it any too well. Suppose,” he continued, “you and Joe come with us. There’s no question but that you’ll like him at once.”

The youths were more than willing, and, led by their fathers, they walked over to a section of the town that was inhabited only by Europeans and Americans.

At a rather attractive-looking house they stopped, and Mr. Lewis knocked on the door.

The door was opened by a large, swarthy man of anywhere between fifty and sixty. One glance at Mr. Lewis and Mr. Holton was enough.

“By Jupiter!” he cried, overjoyed at sight of the naturalists. “Come in, you old rascals.”

Mr. Holton smiled and gave his friend an affectionate pat on the back.

“But we’ve brought our sons with us this time,” he said, indicating Bob and Joe. “George, meet Joe Lewis and Bob Holton. Boys, this is Mr. Seabury.”

There was a shaking of hands and general greeting, and in the end the chums felt perfectly at home.

“Husky fellows,” observed Mr. Seabury. “Look like they could take care of themselves, all right.”

“They certainly can,” affirmed Mr. Lewis, and then outlined some of the boys’ experiences in Brazil, the Sahara, and the Andes Mountains.

Their host listened intently. By the time Mr. Lewis had finished he looked upon the boys with even more respect.

But soon his brow wrinkled.

“Africa is somewhat more dangerous than any of the places they have been,” he said slowly. “There are evidences of that everywhere. In fact, there is evidence of it right here in this house.”

“Referring to yourself, perhaps,” put in Mr. Lewis grimly.

“Just that,” Mr. Seabury returned. “Being charged by a rhino is anything but pleasant. Fortunately, I escaped, but the terrible beast put its mark on me for life.”

There were grim looks on the faces of everyone. Especially were Bob and Joe touched, for they realized for the first time that Africa was a land of tragedy.

“Is there nothing that can be done? Will you always be lame?” inquired Mr. Holton.

Mr. Seabury looked even more grave.

“Medical science cannot help me,” he said at last. “I’m afraid my hunting days are over.” For several moments he retained the same expression. Then suddenly his face lightened, as though he had resolved to forget the matter. “Just what fauna are you after this time?” he asked the naturalists. “But first, before anything more is said, I have something that I want to put before you.”

“What is it, a surprise?” smiled Mr. Lewis.

“Well—you might call it that,” was the response. “Here’s the whole thing: Over six months ago my brother Thomas went into the Congo region to study the primitive tribes there. He was to come back in three months. As yet he hasn’t returned. I fear something has happened to him.”

“That’s too bad,” said Mr. Lewis. “We’ll make it a point to search for him. Just where did he intend to go?”

“It is a very remote region,” Mr. Seabury told them. “Has been called the Forest of Mystery.”

“The Forest of Mystery!” repeated Mr. Holton. “I’ve heard of it. In the central Congo country, isn’t it?”

George Seabury nodded.

“It is said to be full of unexplainable phenomena,” he said. “Has been frequented by only a very few whites.”

Mr. Lewis brought his fist down on the arm of the chair.

“That’s the region we’ll explore,” he said, while Bob’s father nodded. “Have you any idea how to get there?”

“No,” their host responded. “But I know of two natives who have. They live in Mbarara. You men left from there on your last safari in this part of Africa.”

“Yes,” came from Mr. Holton. “But who are these two natives?”

“One is named Noko and the other is Kaika——”

“Kaika!” interrupted Joe’s father. “Why, he was our head bearer on our last safari.”

“That so?” asked Mr. Seabury, somewhat surprised. “Well, he and Noko have been to the Forest of Mystery and know how to get there.”

“Fine.” Mr. Holton smiled happily. “That’s the very place we’ll set out for. And we’ll certainly keep on the lookout for your brother.”

“You don’t know how much it will mean to me if Thomas is found,” said Mr. Seabury. “Of course, I am in no condition to go in search of him, and it would be next to impossible to engage some stranger to do it. So if you will keep on the watch for him, it will certainly ease matters.”

“We’ll be more than glad to do it,” Mr. Lewis told him. “It will be strange if we don’t run across some trace of him.”

For the next hour they talked on indifferent matters. Then, with a parting word, the explorers left Mr. Seabury’s house and went to the hotel.

“Now what?” asked Joe.

The answer was without hesitation.

“We’ll start into the unknown as soon as we possibly can,” said Mr. Holton. “That is, of course, if we can get a train. It may be that we will have to wait several days before one leaves.”

“Boy!” cried Joe, deeply touched. “Into the heart of Africa! I can hardly wait.”