The Hardy Boys, brothers Frank and Joe Hardy, are fictional characters who appear in several mystery series for children and teens. The series revolves around teenagers who are amateur sleuths, solving cases that stumped their adult counterparts.
The Secret of the Old Mill is Volume 3 in the original The Hardy Boys Mystery Stories. The book ranks 86th on Publishers Weekly's All-Time Bestselling Children's Book List for the United States, with 1,467,645 copies sold by 2001. This book is one of the "Original 10", some of the best examples of the Hardy Boys, and Stratemeyer Syndicate writing.
This book was originally written in 1927. Between 1959 and 1973 the first 38 volumes of this series were systematically revised as part of a project directed by Harriet Adams, Edward Stratemeyer's daughter. The original version of this book was rewritten in 1962 by Alistair Hunter resulting in two different stories with the same title.
Visit the posted co ordinates, and look for a plaque on the right hand side of the double doors, containing 10 lines of words/numbers..
Final can be found at 46.AB.CDE and 169.FG.HJK
where
A = third number on the third line
B= number of letters, second word, eighth line
C = second number on the first line
D = last number on the first line
E = number of letters in the first word, tenth line, PLUS 1
F = number of letters, third word tenth line
G = Date on tenth line. XX March 1897. G = X plus X
H = last number on the fifth line, multiplied by 2
J = last number on the sixth line, multiplied by 2
K = number that appears three times on the first line.