When the submarine, called the Advance, was finished, the party made a trip to recover three hundred thousand dollars in gold from a sunken treasure ship, off the coast of Uruguay, South America. They sailed beneath the seas for many miles, and were in great peril at times. One reason for this was that a rival firm of submarine builders got wind of the treasure, and tried to get ahead of the Swifts in recovering it. How Tom and his friends succeeded in their quest, how they nearly perished at the bottom of the sea, how they were captured by a foreign war vessel, and sentenced to death, how they fought with a school of giant sharks and how they blew up the wreck to recover the money is all told of in the book. On their return to civilization with the gold, Mr. Swift, Tom, and their friends deposited the money in the Shopton Bank, where Ned Newton worked. Ned was a bright lad, but had not been advanced as rapidly as he deserved, and Tom knew this. He asked his father to speak to the president, Mr. Pendergast, in Ned's behalf, and, as a result the lad was made assistant cashier, for the request of a man who controlled a three hundred thousand dollar deposit was not to be despised. In building the submarine Tom and his father rented a large cottage on the New Jersey seacoast, but, on returning from their treasure-quest they went back to Shopton, leaving the submarine at the boathouse of the shore cottage, which was near the city of Atlantis. That was in the fall of the year, and all that winter the young inventor had been busy on many things, not the least of which was his storage battery. It was now spring, and seeing the item in the paper, about the touring club prize for an electric auto, had given him a new idea. But all thoughts of electric cars, and everything else, were driven from the mind of the young man, when, with his father, he rushed out to see the cause of the crash on the roof of the Swift homestead. "There's something up there, Tom," called his father, as he splashed on through the rain. "That's right," added his son. "And somebody, too, to judge by the fuss they're making." "Maybe the house has been struck by lightning!" suggested the aged inventor. "No, the storm isn't severe enough for that; and, besides, if the house had been struck you'd hear Mrs. Baggert yelling, Dad. She--" At that moment a woman's voice cried out: "Mr. Swift! Tom! Where are you? Something dreadful has happened!" "There she goes!" remarked Mr. Swift, as he splashed into a mud puddle. "Bless my deflection rudder!" suddenly cried a voice from the flat roof of the Swift house. "Hello! I say, is anyone down there?" "Yes, we are," answered Tom. "Is that you, Mr. Damon?" "Bless my collar button! It certainly is." "Where's Mr. Sharp? I don't hear him." "Oh, I'm here all right," answered the balloonist. "I'm trying to get the airship clear of the chimney. Mr. Damon--"