Biff Norris and the Clue of the Nervous Stranger, by John Runyan (epub/Kindle/pdf)
"John Runyan" was a pseudonym for Bernard Alvin Palmer (1914-1998). Palmer was born in Central City, Nebraska, and he authored more than 165 books for Christian youth, as well as several books for adults. He created numerous series, including the Biff Norris books, the Danny Orlis books, the Felicia Cartright books, and the Pioneer Girls books (which he co-authored with his wife Marjorie Palmer).
His Biff Norris books are designed to appeal to young fans of the Hardy Boys series. They are detective stories, but there is a Christian sensibility infused in the text.