|The Lost Brother|
|House name||Franklin W. Dixon|
|Producer||Simon & Schuster|
|Publication date||October 12, 2010|
|ISBN|| ISBN 1442402563|
|Series|| The Hardy Boys Undercover Brothers|
Lost Mystery Trilogy
|Preceded by||Children of the Lost|
|Followed by||Forever Lost|
|The Hardy Boys Encyclopedia|
Frank has been captured and is held captive in a dark cell. He finds Chloe the candy striper working there. He finds Alice, one of the Misty Falls Lost, who helps him to escape. But he is caught and thrown back in his hail by Baby Doc.
Joe tries to find clues and make progress, but is not much successful. Soon, Justin is captured again. Jacob hires a private investigator, Mr. Smith, to find Justin. Joe is investigating when he sees an atv (all-terrain vehicle) escape. He chases it, but has an accident. He sets up camp and dozes off.
Meanwhile, Frank escapes again. He is caught, and this time has an operation where the criminals try to inject him with a forgetting potion. Alice saves him and tells him that she has found a way out. She leads him and they eventually enter a labyrinth of tunnels. They follow the markers on the walls and reach the exit. Frank manages to escape from the hatch.
Joe wakes up to find a forest fire that has been started by the owner of the atv he had chased. He manages to escape. He follows the rock markers and eventually reaches a place where he hears a sound. It is Frank coming out from the hatch hidden in the ground. Soon, Detective Cole arrives with a rescue team. One of the men is assigned to break the hatch that leads to the underground tunnels with an ax. As soon as he breaks it, an explosion occurs (nobody is killed), but the tunnel gets caved in and the entrance gets blocked.
- Frank Hardy
- Joe Hardy
- Detective Cole
- Bailey Cooper
- Justin Greer
- Jacob Greer
- Mr. Smith (private investigator)
- Dr. Carrini
- Baby Doc
- Scar Guy
- Misty Falls, Idaho
Businesses and organizations
- Happy Land (An Underground Bunker by Dr. Carrini where all the Children of The Lost are kept)
to be added.