The Secret of the Shepherd's Journal (het geheim van het herders dagboek in Dutch) is a Danish comic story serving as a prequel to Atlantis: The Lost Empire, published as part of the Disney Festival series in the Netherlands.
Opening on a meeting at the offices of Whitmore Industries, Rourke and Helga are called in by Whitmore to be told of their preparations for their latest expedition, waiting on Thaddeus Thatch to arrive to give them the specifics of the mission. Arriving late and rather excitedly, Thatch explains that he has closed in on the location of the Shepherd's Journal. After telling the Journal's history from its creation by the shepherd Aziz and its journey around the world and through history, he explains that it has been quietly sneaked away to Iceland and hidden away in the headquarters of the Keepers of the Journal, a secret society that has been trying to keep the book's secrets hidden from the world. After finishing his story, Thatch makes his wager with Whitmore to finance the expedition to Atlantis itself if the Journal actually materializes. The group leaves to make final preparations with Thatch going to the Library of Congress to compare his findings with older research on the same subject while Rourke and Helga go to the train station to meet Vinny, Mole and Luis (Audrey Ramirez's father).
However, Thatch is followed by a pair of thugs interested in rumors of the expedition's goals and is taken hostage. After hearing the news that Thaddeus is missing, Rourke and the crew go to his apartment to find it ransacked. After Mole analyzes dirt found on the scene, the crew finds the kidnappers's hideout at an abandoned horsetrack. Helga takes out the kidnappers and Thaddeus leads the group to a park near the Library where he hid his research journal under a statue of Abraham Lincoln. However, the kidnappers managed to come to and flatten the tires of the car the team came in. Luis manages to fix an old truck to get back to the park and recover the journal, but the kidnappers are there waiting for them, revealing they only took an interest in the expedition knowing that whatever Rourke was hired to find would be worth a fortune. Though Vinny is able to use an explosive as a distraction for Helga to disarm one of the criminals, the other one is still able to coerce the team into giving them the journal by holding Luis at gunpoint. Thatch complies and they make their getaway, but he reveals that he had already removed the last page with the journal's location during the confusion, allowing them to proceed to Iceland.
- Atlantis: Search for the Journal, which depicts the Iceland expedition itself.