The year is 1899, but on this alternate Earth, the great nations of Europe are on the brink of war as new weapons are being developed. In London, a group of cops is shocked when they see the first tank crash into the Bank of England, destroying everything in the rooms while being unaffected by bullets. The tank uses its cannon to shoot the vault door open before the terrorists come out with their leader the Fantom.
There are lots of treasures in the vault, but what the Fantom wants are the blueprints of Venice’s foundation. Britain accuses Germany of the robbery, but soon afterward, the Fantom and his men show up in Berlin, where they kidnap a bunch of scientists and blow up all the zeppelins. Countries begin pointing fingers at each other and war is imminent.
Sometime later in Kenya, Reed is looking for Allan, the famous hero from “King Solomon's Mines”. An old man calling himself Allan starts sharing some old adventure stories, but when Reed mentions he works for the British government and they need help, the real Allan reveals himself. It turns out he often uses a friend to protect his identity.
Reed explains he’s trying to prevent the next world war, but Allan refuses to help because he doesn’t fight anymore since he lost his family. At that moment, a group of strange men come in and ask for Allan, only to shoot the old man thinking he’s the real one. Allan immediately opens fire and a gunfight ensues, but it’s hard to kill these guys because they’re wearing armor and using the latest model of guns, which are automatic.
After a few very precise shots to make the men fail, Allan comes out to fight them hand to hand, dodging bullets and knives to defeat the bad guys using furniture and even a horn on the wall. One of the henchmen manages to run away so Allan goes after him, not noticing the suitcase they left behind. Since he’s an expert sharpshooter, Allan stops the guy by shooting from afar, but before he can interrogate, the guy self-deletes with poison.
Suddenly the tavern explodes, and since the war is threatening the peace he achieved in Africa, Allan accepts to help Reed. Later in England, Reed introduces Allan to his boss M, who explains he’s forming a team known as the “League of Extraordinary Gentlemen” to stop the Fantom. Allan also meets Captain Nemo from “Twenty Thousand Leagues Under the Seas”, whose ship will take them to Venice in four days because clues indicate the Fantom will attack there next.
Suddenly a voice talks from an empty chair and some papers start moving: it turns out the other team member is Skinner, a thief who made a serum to become invisible but hasn’t found a cure yet. To be less annoying, Skinner puts on a jacket and face paint so the others can see him. At that moment, another team member arrives: her name is Mina and she’s an expert chemist, but Allan isn’t happy about having a woman on the team.
The group gets going and Nemo impresses everyone with the latest automobile technology. The driver is his first mate Ishmael, from “Moby Dick”. On their way out, they don’t notice they’re being followed.
Eventually they make it to the docks to recruit the infamous Dorian Gray, who only lets them in because Mina is his ex. After noticing that Dorian is missing a painting on the wall, Allan shares that a witch doctor once blessed him for saving the village, so it’s said Africa will never let him die. He also remembers meeting Dorian when he was a child, yet Dorian hasn’t aged a day.
Dorian avoids all explanations because he isn’t interested in joining the team, but the conversation is interrupted when a bunch of armed men come out of the shadows together with the Fantom, who asks the league to join him. While the Fantom talks, Allan notices one of the henchmen looks different: he’s the stalker from earlier, who immediately opens fire against the enemy. Chaos ensues in the room as everyone begins to fight and reveals their skills in the process: Dorian is immortal, so he just walks into the bullets to kill the men with his sword and lets his body heal himself.
Nemo uses a sword and martial arts while Allan uses his own firearm and so does the stalker, who turns out to be an American secret service agent called Tom Sawyer. Skinner takes off his jacket and paint to hit bad guys with things like books. The Fantom runs away and Allan tries to stop him, but he’s intercepted by a henchman.
While they fight, Tom tries to chase after the Fantom, who manages to escape by jumping through the window into the river. The guys think the fight is over, but there’s one last man hiding and he takes Mina hostage. However Mina’s eyes suddenly turn red and she bites the guy to kill him by drinking his blood.
It turns out she’s the widow of Jonathan Harker, who was part of the team that killed Drcula. Then Dorian accepts to join the team because he took this attack personally, and Allan lets Tom join too. Tom was sent by the American government because they're worried the war will reach the Americas too.
The team’s next stop is Paris, so Nemo introduces the team to his ship Nautilus, which can also work as a submarine. When they finally arrive at the city, Allan and Tom chase after a huge monster known as Mister Hyde, who has been terrorizing the locals lately. With calculated shots, Allan lures Hyde into a very specific spot while teaching Tom how to waste fewer bullets, calling his crazy shooting “American Style”.
Hyde eventually stops on a rooftop and Allan shoots to make him fall right into a net they prepared earlier. Once they make it back to Nautilus, it requires lots of crew members to chain Hyde down, and yet the monster still manages to push some of them away. While they try to calm him down, Skinner falls and Dorian helps him, only to scratch him in the process.
Allan manages to make Hyde stop by offering a deal: if he helps them, he’ll get a pardon from the Queen and he can go back to London. Hyde accepts and at that moment, the effects of the elixir he took to transform finally end and he painfully transforms into his real form: the very shy Doctor Jekyll. Now the team is complete, the ship enters submarine mode and starts making its way to Venice using a copy of the blueprints the Fantom stole.
Now the team has to learn to live with each other: Allan is soon annoyed by Skinner because he doesn’t wear his coat to make his presence known, and Mina is disturbed to learn that Nemo worships the Goddess of Death. However Allan is more scared of her than some religious statue. One afternoon after the Nautilus enters ship mode again, Allan tries to teach Tom how to waste fewer bullets and shoot more accurately, but when Tom asks him about his dead son, Allan leaves.
Meanwhile Nemo and Ishmael are surprised to find powder in the control room right before a book closes on its own behind them. They give the powder to Mina, who analyses it and discovers that it’s the powder photographers use to create flash. Dorian visits her and shares his secret: the missing portrait at his home is magical, and it ages instead of him.
He can’t look at it or he’ll lose his powers. Dorian also flirts with Mina and shares a drink, but when the glass breaks, it cuts her finger. The smell of blood gets Mina excited and they end up kissing, which makes Jekyll jealous while he watches from afar.
His inner Hyde reminds him he could be noticed by women if he drank the elixir again and he even gets aggressive, but before he can lose control, Nemo interrupts him. The captain says he doesn’t want a monster loose in his ship, and Jekyll reminds him that he has a dark past as a pirate so he can’t talk. Then Jekyll returns to his room and is shocked to discover one of his elixir bottles is missing.
He immediately lets Allan know and accuses Skinner of stealing it since none of them have heard from him in a while. When they finally arrive at Venice, there’s a carnival going on, and by looking at the blueprints the team guesses the Fantom will be blowing up the city. The league gets ready to start searching for the explosives, but as soon as they touch land, the bombs go off and the buildings start crumbling in a domino effect.
They must destroy a particular building to stop it, so Tom takes Nemo’s automobile and leaves with Allan, Dorian, and Mina, but Jekyll refuses to go because he’s afraid of releasing Hyde. As soon as the team drives down the streets, the Fantom’s men surround them and open fire. Dorian thinks Skinner let them know they were coming and runs away.
Allan and Tom try to shoot back but there are too many men, so Mina jumps out of the car and climbs the wall with her powers to quickly feed on all the bad guys without mercy. While buildings continue to collapse and start damaging the ship, Allan sees the Fantom nearby and he jumps out as well to go after him. Tom is left driving alone and after dodging lots of falling debris, he finally finds the right building and shoots a flare, so Nemo fires a rocket that destroys that building and finally puts an end to the domino effect.
As the explosion goes off, the car flips and Tom gets caught under it. On the ship, Dorian reveals he’s the actual spy and shoots Ishmael. Meanwhile, Allan follows the Fantom to a cemetery and they exchange a few hits.
The Fantom stabs Allan on the shoulder and Allan hits him in return, which causes the mask to fall and shows his identity. He’s actually M, which stands for Moriarty, the legendary enemy of Sherlock Holmes. The Fantom runs away and Allan throws the knife back at him, but it isn’t enough to stop him.
Afterward, the team returns to the ship and finds a dying Ishmael, who uses his last breath to tell them about Dorian. At that moment, the ship’s exploration pod comes out and shows Dorian going away to meet with the Fantom. The league immediately starts following him with the ship, and during the trip, they find a recording left by Dorian.
The Fantom's voice starts playing, explaining that Reed works for him too and he sent him to put together the league on purpose so Dorian could get a sample of their abilities. Dorian stole Jekyll’s elixir bottle, took Mina’s blood with the broken glass, took Skinner’s skin when he scratched him, and took pictures of Nemo’s technology. Allan was recruited because he was the only one capable of capturing Hyde.
With these samples, he’ll able to build super soldiers to sell during wartimes. As he listens, Jekyll notices his inner Hyde is in pain because of a weird frequency in the recording, and at that moment the Fantom announces the ship will explode when the recording ends. That’s exactly what happens, and the entire ship shakes as water starts to flood the engine room and drags down some crew members.
Nemo can’t make the Nautilus resurface because of this, so he orders his men to seal the engine room with the men inside for the greater good. Hyde convinces Jekyll they can help, so he runs into the room before it’s sealed and takes the elixir to transform underwater. Then he swims down to the bottom and using his strength, he pulls the levers and opens the valves, which immediately drains the ship and allows it to resurface.
While everyone tries to organize things, they get a message in Morse code from Skinner, who sneaked into the pod with Dorian and now sends the team directions to follow. Eventually they make it to Northern Mongolia, where they discover the Fantom’s secret fortress. They hide in a cave to wait for Skinner, who arrives with a disturbing report: the fortress is huge and the kidnapped scientists are working in factories 24/7 to make supersoldiers and copy Nemo’s inventions.
While the team makes a plan, Dorian asks the Fantom for his painting, revealing that the Fantom stole it just to make him work for him. Now that he has it back, Dorian refuses to fight again. Soon the league arrives at the fortress and they knock down the guards outside with their powers.
They sneak inside and Skinner begins placing explosives around the factory while Hyde, Nemo, and his crew free the families of the scientists, but unfortunately they’re found by a whole army of guards. A gunfight soon ensues, but Nemo’s weapons don’t do anything because the enemy is wearing full body armor. Hyde uses a huge metal door to deflect the bullets, giving Nemo the chance to fight the guards at the lab with his sword and release the scientists too.
Meanwhile, Mina finds Dorian in his room and they begin a fight with blades, but no matter how much they slash at each other, their wounds keep regenerating. Suddenly Mina is distracted when she notices the magical painting, so Dorian uses the chance to nail her to the bed with his sword. However he fails to get her heart, so Mina surprises him from behind and impals him on the wall with his own sword.
Then she forces him to look at his painting, which breaks the spell and Dorian regains all the years the picture took from him until he dies. Allan and Tom go looking for the Fantom, who is currently overseeing the box with all the league’s samples. They manage to corner him, but unfortunately a guard catches them from behind and they have to dodge an attack, which allows the Fantom to escape with the box.
The duo immediately goes after him, and in one of the corridors they bump into an invisible man who suddenly attacks them because he isn’t Skinner. While Allan continues to chase the Fantom, Tom stays to fight this new invisible man, but he continues to waste too many bullets. At that moment an armored soldier arrives and uses a flamethrower to start burning everything in the room, but this time, the real Skinner distracts him and ends up on fire too.
Tom quickly uses the chance to hit the guy with a torch, causing the gas tank to blow up and kill him. Afterward Tom checks on a burnt Skinner, only to be caught by the other invisible man. At the same time, Allan finds the Fantom in a dark room and they begin to fight, exchanging a bunch of hits until Fantom falls and Allan grabs an axe, ready to end it all.
Back to Nemo, he manages to get all the scientists out while Hyde protects them, but one of the guards steals some elixir from the lab and drinks more than he should. He transforms into such a powerful monster that Hyde and Nemo have trouble fighting against him even while teaming up. At that moment Hyde changes back into Jekyll, so he and Nemo have to run.
The monster and Allan are about to make their kills at the same time but suddenly Skinner’s explosives go off and the building starts to crumble. Hyde and Nemo run outside while the monster is killed by the falling debris, meanwhile the Fantom uses the distraction to dodge Allan’s attack. When Allan tries to stop him again, the Fantom shows him that his invisible man has caught Tom, so Allan turns to save his protegee and the Fantom stabs him in the back before jumping out of the building.
Since Allan’s glasses are now broken, Tom takes Allan’s rifle and using his teachings, he manages to kill the Fantom from a distance. While the box with the samples is lost in the water, Allan tells Tom that the new century belongs to the new generation, and then he dies too. Sometime later, the league buries Allan with his family in Africa, and Tom leaves the rifle on the grave.
The group decides to keep being a team and leave to start a new adventure. Once they’re gone, the witch doctor from Allan’s story comes to start his ritual, which makes the grave shake.
