Either taking place in 1910s Washington DC, or 1910s London, Milo James Thatch is a young cartographer and linguist who hopes to fulfill his late grandfather's dream of finding the fabled lost city of Atlantis. But the museum he works in won't help provide for an expedition, believing Milo's grandfather (Thaddeus Thatch) was a loon. After coming home, Milo receives a visit from a mysterious woman (Lieutenant Helga Sinclair) who tells him that her employer has a proposition for him. Milo meets eccentric billionaire Preston Whitmore, Thaddeus' former partner, who gives Milo the one thing that Thaddeus found the year before he died: The Shepherd's Journal, an unpublished book filled with knowledge about the list city. The book is used as a map to find Atlantis. The kind professor funds the expedition along with a much needed crew: Vinnie (an Italian demolitionist), Moliere (a French geologist with mole-like instincts), Audrey (a Mexican teen-aged engineer), Dr. Joshua Sweet (a medical officer), Cookie (a chuck wagon chef), Mrs. Packard (a cantankerous communications officer), Lieutenant Sinclair, and Naval Commander Lyle Rourke (who led Thaddeus' exploration team that found the Journal). Upon diving in their submarine, the Ulysses, the explorers get attacked by a sea monster, causing casualties, until eventually, they find an underground chamber that guaranteed to reach Atlantis.
