While returning from a country carnival, Nancy, Bess, and George witness the malicious burning of a stately home.
Fearing its occupants might be trapped in the fire, the girls rush to the rescue.
During all the commotion, Nancy notices a mysterious man running from the fire, and finds a diary that had been lost.
Nancy learns the homeowner and the man who kept the diary are involved in a business transaction in which the latter was cheated.
Despite strong evidence to the contrary, Nancy is convinced of the prime suspect’s innocence.
While working to exonerate the troubled man, Nancy is delighted by her new friendship with the handsome Ned Nickerson, another passing motorist who stopped to help.