The Secret of the Old Mill is Volume 3 in the original Hardy Boys series of mystery books for children and teens published by Grosset & Dunlap. The Hardy boys are determined to learn the secret of an old mill and employ a clever ruse to gain entrance. But soon they are trapped.
In this adventure, there is danger on two levels for Frank and Joe. First, they confront a nasty gang who will stop at nothing to halt their investigations and second, their father Denton Hardy is on a confidential mission that may deal with sabotage. Will the Hardys unravel the mysteries?
Frank and Joe Hardy and their friend Chet Morton wait at a train station in their hometown of Bayport for Frank and Joe’s father. While there, they see a man jump on a departing train. Frank is 18, and Joe is 17. Their father is a famous detective and is returning from a business trip to Detroit. When he doesn’t arrive, the brothers assume he has been unexpectedly delayed and plan to meet a later train. In the meantime, the three friends go into town to pick up Chet’s new microscope.
Ken Blake, a teenager who works as a bicycle errand boy, is almost hit by a car. Frank, Joe and Chet help him. Joe gives Ken an envelope he dropped, noticing it is labeled confidential and is addressed to Victor Peters. Ken thanks the boys but is vague about where he works. Frank inspects Ken’s bike, and Ken tells him it came from Belgium.
