A big fish contest at The Trading Post, the Hollisters’ sporting goods store, has everybody in Shoreham excited. After Pete catches a large fish with a tag on its tail, another adventure begins for the eager young detectives. When the children’s friend, Bobby Reed, disappears in a leaky old boat, the whole family helps in the search. Uncle Russ lends them his boat, and they set off on a trip down the Muskong River. After helping some hikers on shore, Pete, Pam and Mr. Hollister get lost in the fog on their way back to the boat. A series of surprise discoveries lead the Hollisters on a hunt for Bobby on shore, and other adventures provide good times along the way. But there are false clues and disappointments before the Hollisters find Bobby, solve the mystery of the tagged fish, and bring happiness to an old man, Bobby and his mother.