As Bert, Nan, and Harry were getting in Mr. Blackford's automobile to go to Meadow Brook Farm, Bob Guess came hurrying up through the rain. The merry-go-round, as well as other amusements at the fair, had shut down on account of the storm. "Where's your father?" asked Bob of Bert. "I've something to tell him. Where is he?" "He's gone off after the balloon. Flossie and Freddie are in it," Nan answered. "Whew! Those little children taking a balloon ride!" cried Bob. "How did they dare?" "It was an accident," Harry explained. "They didn't mean to." "Well, tell your father I want to see him when he gets back," said Bob, as he hurried back to the merry-go-round. "I have something to tell him about Mr. Blipper." However, Bert and Nan had other things to think about then than about Mr. Blipper. They were worried over what might happen to Flossie and Freddie. Meanwhile, Mr. and Mrs. Bobbsey were hastening toward the lake. Mr. Bobbsey drove his car as fast as he dared through the storm. It was now raining hard. "How long would the balloon stay up in the air?" asked Mr. Bobbsey of Mr. Trench. "It all depends. On a hot day, when the sun warms the gas, it would stay up a long time. But when it is cool, like this, and rains, it will not stay up so long. It will come down gently, and I am sure the children will not be hurt." As they drove along they stopped now and then to ask people if they had seen the runaway balloon. Many had, and all said it was sailing toward the lake. When the lake was reached and a motor-boat had been found which would take them out on the water, several men said they had seen the big gas bag beginning to go down near Hemlock Island, the largest island in the lake. "If they have only landed there they may be all right," Mrs. Bobbsey said. "Oh, hurry and get there, Dick!" "We'll hurry all we can," her husband told her, as they got into the boat to continue the search. "But this is a bad storm. We must be careful." CHAPTER XVIII ON THE ROCKS The whole world seemed a very dreary and unhappy place to Mr. and Mrs. Bobbsey as they started off in the motor-boat to look for Flossie and Freddie. In the first place, if one of the little Bobbsey twins had just been lost--plain lost--as Flossie was in the cornfield, it would have been sad enough. But when both tots were missing, and when the last seen of them had been a sight of them shooting away in a balloon through a gathering storm, well, it was enough to make any father and mother feel very unhappy. Besides this, there was the rain, and as the motor-boat, in charge of Captain Craig, swung out into the lake, the big, pelting drops came down harder than ever. "Oh, what a sad, sad day!" sighed Mrs. Bobbsey. "And it started off so happily, too!" "Perhaps it will end happily," said Mr. Bobbsey, hopefully. "It will not be night for several hours yet, and before then we may find Flossie and Freddie. In fact I'm sure we shall!"