all at once it grew dark around them. neither cap'n bill nor trot liked this gloom, for it made them nervous not to be able to see their enemies.

"we must be near a sea cavern, if not within one," whispered princess clia, and even as she spoke the network of scarlet arms parted before them, leaving an avenue for them to swim out of the cage. there was brighter water ahead, too, so the queen said without hesitation:

"come along, dear friends; but let us clasp hands and keep close together."

they obeyed her commands and swam swiftly out of their prison and into the clear water before them, glad to put a distance between themselves and the loathesome sea devils. the monsters made no attempt to follow them, but they burst into a chorus of harsh laughter which warned our friends that they had not yet accomplished their escape.

the four now found themselves in a broad, rocky passage, which was dimly lighted from some unknown source. the walls overhead, below them and at the sides all glistened as if made of silver, and in places were set small statues of birds, beasts and fishes, occupying niches in the walls and seemingly made from the same glistening material.

the queen swam more slowly now that the sea devils had been left behind, and she looked exceedingly grave and thoughtful.

"have you ever been here before?" asked trot.

"no, dear," said the queen with a sigh.

"and do you know where we are?" continued the girl.

"i can guess," replied aquareine. "there is only one place in all the sea where such a passage as that we are in could exist without my knowledge, and that is in the hidden dominions of zog. if we are indeed in the power of that fearful magician, we must summon all our courage to resist him, or we are lost!"

"is zog more powerful than the mermaids?" asked trot anxiously.

"i do not know, for we have never before met to measure our strength," answered aquareine. "but if king anko could defeat the magician, as he surely did, then i think i shall be able to do so."

"i wish i was sure of it," muttered cap'n bill.

absolute silence reigned in the silver passage. no fish were there; not even a sea flower grew to relieve the stern grandeur of this vast corridor. trot began to be impressed with the fact that she was a good way from her home and mother, and she wondered if she would ever get back again to the white cottage on the cliff. here she was, at the bottom of the great ocean, swimming through a big tunnel that had an enchanted castle at the end, and a group of horrible sea devils at the other! in spite of this thought, she was not very much afraid. although two fairy mermaids were her companions, she relied, strange to say, more upon her tried and true friend, cap'n bill, than upon her newer acquaintances to see her safely out of her present trouble.

cap'n bill himself did not feel very confident.

"i don't care two cents what becomes o' me," he told princess clia in a low voice, "but i'm drea'ful worried over our trot. she's too sweet an' young to be made an end of in this 'ere fashion."

clia smiled at this speech. "i'm sure you will find the little girl's end a good way off," she replied. "trust to our powerful queen, and be sure she will find some means for us all to escape uninjured."

the light grew brighter as they advanced, until finally they perceived a magnificent archway just ahead of them. aquareine hesitated a moment whether to go on or turn back, but there was no escaping the sea devils behind them, and she decided the best way out of their difficulties was to bravely face the unknown zog and rely upon her fairy powers to prevent his doing any mischief to herself or her friends. so she led the way, and together they approached the archway and passed through it.

they now found themselves in a vast cavern, so great in extent that the dome overhead looked like the sky when seen from earth. in the center of this immense sea cavern rose the towers of a splendid castle, all built of coral inlaid with silver and having windows of clear glass.

surrounding the castle were beds of beautiful sea flowers, many being in full bloom, and these were laid out with great care in artistic designs. goldfish and silverfish darted here and there among the foliage, and the whole scene was so pretty and peaceful that trot began to doubt there was any danger lurking in such a lovely place.

as they approached to look around them, a brilliantly colored gregfish approached and gazed at them curiously with his big, saucer-like eyes. "so zog has got you at last!" he said in a pitying tone. "how foolish you were to swim into that part of the sea where he is powerful."

"the sea devils made us," explained clia.

"well, i'm sorry for you, i'm sure," remarked the greg, and with a flash of his tail, he disappeared among the sea foliage.

"let us go to the castle," said the queen in a determined voice. "we may as well boldly defy our fate as to wait until zog seeks us out."

so they swam to the entrance of the castle. the doors stood wide open, and the interior seemed as well lighted as the cavern itself, although none of them could discover from whence the light came.

at each side of the entrance lay a fish such as they had never seen before. it was flat as a doormat and seemed to cling fast to the coral floor. upon its back were quills like those of a porcupine, all pointed and sharp. from the center of the fish arose a head shaped like a round ball, with a circle of piercing, bead-like eyes set in it. these strange guardians of the entrance might be able to tell what their numerous eyes saw, yet they remained silent and watchful. even aquareine gazed upon them curiously, and she gave a little shudder as she did so.

inside the entrance was a domed hall with a flight of stairs leading to an upper balcony. around the hall were several doorways hung with curtains made of woven seaweeds. chairs and benches stood against the wall, and these astonished the visitors because neither stairs nor chairs seemed useful in a kingdom where every living thing was supposed to swim and have a fish's tail. in queen aquareine's palaces benches for reclining were used, and stairs were wholly unnecessary, but in the palace of zog the furniture and fittings were much like those of a house upon earth, and except that every space here was filled with water instead of air, trot and cap'n bill might have imagined themselves in a handsome earthly castle.

the little group paused half fearfully in the hall, yet so far there was surely nothing to be afraid of. they were wondering what to do next when the curtains of an archway were pushed aside and a boy entered. to trot's astonishment, he had legs and walked upon them naturally and with perfect ease. he was a delicate, frail-looking little fellow, dressed in a black velvet suit with knee breeches. the bows at his throat and knees were of colored seaweeds, woven into broad ribbons. his hair was yellow and banged across his forehead. his eyes were large and dark, with a pleasant, merry sparkle in them. around his neck he wore a high ruff, but in spite of this trot could see that below his plump cheeks were several scarlet-edged slits that looked like the gills of fishes, for they gently opened and closed as the boy breathed in the water by which he was surrounded. these gills did not greatly mar the lad's delicate beauty, and he spread out his arms and bowed low and gracefully in greeting.

"hello," said trot.

"why, i'd like to," replied the boy with a laugh, "but being a mere slave, it isn't proper for me to hello. but it's good to see earth people again, and i'm glad you're here."

"we're not glad," observed the girl. "we're afraid."

"you'll get over that," declared the boy smilingly. "people lose a lot of time being afraid. once i was myself afraid, but i found it was no fun, so i gave it up."

"why were we brought here?" inquired queen aquareine gently.

"i can't say, madam, being a mere slave," replied the boy. "but you have reminded me of my errand. i am sent to inform you all that zog the forsaken, who hates all the world and is hated by all the world, commands your presence in his den."

"do you hate zog, too?" asked trot.

"oh no," answered the boy. "people lose a lot of time in hating others, and there's no fun in it at all. zog may be hateful, but i'm not going to waste time hating him. you may do so, if you like."

"you are a queer child," remarked the mermaid queen, looking at him attentively. "will you tell us who you are?"

"once i was prince sacho of sacharhineolaland, which is a sweet country, but hard to pronounce," he answered. "but in this domain i have but one title and one name, and that is 'slave.'"

"how came you to be zog's slave?" asked clia.

"the funniest adventure you ever heard of," asserted the boy with eager pride. "i sailed in a ship that went to pieces in a storm. all on board were drowned but me, and i came mighty near it, to tell the truth. i went down deep, deep into the sea, and at the bottom was zog, watching the people drown. i tumbled on his head, and he grabbed and saved me, saying i would make a useful slave. by his magic power he made me able to live under water as the fishes live, and he brought me to this castle and taught me to wait upon him as his other slaves do."

"isn't it a dreadful, lonely life?" asked trot.

"no indeed," said sacho. "we haven't any time to be lonely, and the dreadful things zog does are very exciting and amusing, i assure you. he keeps us guessing every minute, and that makes the life here interesting. things were getting a bit slow an hour ago, but now that you are here, i'm in hopes we will all be kept busy and amused for some time."

"are there many others in the castle besides you and zog?" asked aquareine.

"dozens of us. perhaps hundreds. i've never counted them," said the boy. "but zog is the only master; all the rest of us are in the same class, so there is no jealousy among the slaves."

"what is zog like?" cap'n bill questioned.

at this the boy laughed, and the laugh was full of mischief. "if i could tell you what zog is like, it would take me a year," was the reply. "but i can't tell you. every one has a different idea of what he's like, and soon you will see him yourselves."

"are you fond of him?" asked trot.

"if i said yes, i'd get a good whipping," declared sacho. "i am commanded to hate zog, and being a good servant, i try to obey. if anyone dared to like zog, i am sure he'd be instantly fed to the turtles; so i advise you not to like him."

"oh, we won't," promised trot.

"but we're keeping the master waiting, and that is also a dangerous thing to do," continued the boy. "if we don't hurry up, zog will begin to smile, and when he smiles there is trouble brewing."

the queen sighed. "lead the way, sacho," she said. "we will follow."

the boy bowed again, and going to an archway, held aside the curtains for them. they first swam into a small anteroom which led into a long corridor, at the end of which was another curtained arch. through this sacho also guided them, and now they found themselves in a cleverly constructed maze. every few feet were twists and turns and sharp corners, and sometimes the passage would be wide, and again so narrow that they could just squeeze through in single file. "seems like we're gettin' further into the trap," growled cap'n bill. "we couldn't find our way out o' here to save our lives."

"oh yes we could," replied clia, who was just behind him. "such a maze may indeed puzzle you, but the queen or i could lead you safely through it again, i assure you. zog is not so clever as he thinks himself."

the sailor, however, found the maze very bewildering, and so did trot. passages ran in every direction, crossing and recrossing, and it seemed wonderful that the boy sacho knew just which way to go. but he never hesitated an instant. trot looked carefully to see if there were any marks to guide him, but every wall was of plain, polished marble, and every turning looked just like all the others. suddenly sacho stopped short. they were now in a broader passage, but as they gathered around their conductor they found further advance blocked. solid walls faced them, and here the corridor seemed to end.

"enter!" said a clear voice.

"but we can't!" protested trot.

"swim straight ahead," whispered the boy in soft tones. "there is no real barrier before you. your eyes are merely deceived by magic."

"ah, i understand," said aquareine, nodding her pretty head. and then she took mayre's hand and swam boldly forward, while cap'n bill followed holding the hand of clia. and behold! the marble wall melted away before them, and they found themselves in a chamber more splendid than even the fairy mermaids had ever seen before.