In an alternate Victorian Age, the world is facing a grave threat from a mysterious villain known only as "The Phantom", who seeks to ignite a world war with fantastical technologies well beyond the era's own. To counter this menace, British government agent Campion Bond recruits the legendary adventurer Allan Quatermain to lead a unique team of individuals with extraordinary abilities. This team includes Captain Nemo, commander of the advanced submarine Nautilus; Mina Harker, a woman with dark secrets and vampiric abilities; Rodney Skinner, an invisible thief; Dorian Gray, an immortal dandy with a deadly touch; Tom Sawyer, now a secret service agent; and Dr. Henry Jekyll, who harbors his violent alter ego, Edward Hyde. These individuals, known for their remarkable traits and exploits, must set aside their solitary nature to work together.

As the newly formed league gathers, they set out on their first mission to investigate the destruction of a German city, attributed to The Phantom. Their journey takes them to the heart of the threat in Venice, where the mysterious figure plans to strike at a gathering of world leaders. Here, each member is tested, as they encounter advanced weaponry and numerous dangers, challenging both their abilities and their willingness to operate as a team. The group's cohesion is strained by internal conflict and the secrets they keep from one another, which threaten to unravel their alliance at a time when unity is most crucial.