Summary.  This book consists of two unrelated stories, with a two chapter short story fill-in between them.  The first story consists of chapters 1-11, and relates incidents around the arrival of a showboat on the river bank.  The boys get a motor on the houseboat that Mr. Lanigan had given them, and make money by ferrying people to and from the showboat.  Then chapters 12-13 relate a brief interlude with the boys camping in a tent.  Chapters 14-44 tell the story of Gander, a boy with a gang in Watertown.  They come down to the river bank, causing all kinds of trouble: whipping the Pelham boys, fighting with the Club boys, stealing, and serious acts of vandalism. 

The newspaper stories comprising Gander were published shortly after the famous 1937 flood on the Ohio River, which was at its peak in late January 1937.  A record-breaking flood occurs in this book as well. 

Gander falls very ill during the flood, and the kindness and help provided by Hawkins cause him to reform and become a good boy.  He disbands his gang and urges them to live better lives, too.  Gander had a knack for training and taking care of pet owls, resulting in him getting a job with Old Hiram, and the book ends with the two of them headed off to Africa on an animal-collecting trip.