Hal wakes up and finds himself plummeting toward a planet. He uses his ring to protect himself just as he slams into the middle of a city street. Hal is unable to contact his teammates on his ring, and as he looks around he discovers that the pedestrians are wearing 19th Victorian clothing. A woman, Lady Catherine, is on a street corner protesting the tyranny of Duke Nigel Fortenberry. Steam-powered robots march down the street and order the people to comply with the law or face prison. Lord Nigel speaks through the robots, insisting that he saved the planet and they must do what he says.
As the robots advance on Catherine, a man wearing a rocket pack flies down and knock down the robots by firing a beam of green energy. The people cheer their hero as Hal stares in surprise. The robots recover and advance on the "Steam Lantern," and Hal comes to the aid of the new hero. He makes short work of the robots and the new hero picks up Catherine and tells Hal to follow them. They fly up into the clouds to a vast floating base suspended from a dirigible. Catherine introduces her companion as Gil Broome and Gil is surprised to discover that Hal is a real Green Lantern. He explains that he's a Steam Lantern and modeled himself after a Green Lantern who wore a red shirt and a cape. Catherine is the one who built the dirigible and the suit that Gil wears, and they're all powered by hardtofindium.
When Hal asks about Duke Nigel, his new friends explains that the stars in their world started winking out one by one. Duke Nigel promised to save them but turned the world into an industrial nightmare ever since. Catherine mentions that Duke Nigel tried to frighten them by allying himself with the Anti-Monitor. Gil hit it hard enough to send the Anti-Monitor through a rip between worlds. Hal realizes that he's in the other world and they suggest that he access the electro-power in Nigel's lab so he can contact his friends in the other universe.
The two Lanterns and Catherine fly to Nigel's lab and they discover that Nigel is keeping a careful eye on the sun. Catherine access the communication systems and Hal starts to send a signal.
In the other universe, Kilowog insists that Hal is still alive but Tomar-Re isn't so sure. Hal makes contact with them and explains what happened. Tomar-Re warns that he will need monumental power to go through the portal but Hal points out that the unknown Green Lantern did it. He tells his comrades to contact him in 12 hours and signs off. Nigel's robots attack and capture the three heroes. Nigel comes in and insists that he only wants credit for saving their world, blaming Steam Lantern for stealing his glory.
Hal frees himself and defeats the robots, and then warns Nigel that he'll bring the place down if he bothers his friends again. They return to the dirigible and Catherine assures Gil that he did his part and that he will still be there when Hal returns to his universe. As she goes to prepare for an ascent into the stratolayer, Gil tells Hal that Nigel did save the planet. The Anti-Monitor was consuming the planet and Nigel made a deal with him by showing him how to access another universe. Nigel drove his world on an industrial spree to create the machinery necessary, and Gil fought back without knowing about Nigel's deal. However, the Anti-Monitor didn't even notice. Nigel fired his own beam sending the Anti-Monitor away but everyone thought Gil was the one who did it. Gil asks Hal to stay and fight Duke Nigel, but Hal says that he has to deal with the menace in his universe. He assures Gil that he has what it takes to be a hero. Catherine returns and assures Hal that that Gil can handle anything that they need to and they head up into the sky.
Aya takes the interceptor to the rip in space above Biot and waits for Hal's signal.
The dirigible reaches its limits and Hal thanks them for their help. He flies toward the rift and hits it with everything he has. Gil flies up and lends his power to Hal's and the rift opens. On the other side, Aya detects the rift opening and Kilowog adds his own beam energy to their efforts.
Duke Nigel flies up in a gyrocopter and orders Catherine to surrender. Gil flies down to deal with his nemesis while Hal continues his efforts. Stray shots hit the dirigible, setting it on flame and causing it to go down. Hal realizes what is happening and flies down to help, catching it just in time before it smashes into the city. Gil goes to Catherine and makes sure that she's okay. Nigel aims his guns at Catherine and Gil and warns Hal that he can kill them before he can do anything, and Hal reluctantly surrenders.
Nigel takes his prisoners back to his lab and insists that he's doing what he has to so he can protect his world. When Catherine defends her beau, Gil says that he's had enough and that he will tell the world the truth about Nigel. Catherine protests, telling him not to lie to save her, but Gil says that it's the truth. Nigel agrees to release Catherine after Gil's confession and frees Steam Lantern. Gil broadcasts his confession worldwide, admitting that he enjoyed the glory. Catherine assures him that she loved him regardless. The people start cheering Gil, much to Nigel's surprise, and Hal explains that Gil is a hero for fighting against tyranny. Nigel insists that he simply built his robots to spread the news and that he's no villain, but realizes that he unwittingly turned them against the people. He tells his men to release everyone.
The sun dims and Nigel explains that the Anti-Monitor ate most of the nuclear fuel in their sun. Nigel only put off his world's destruction for a few months while dooming trillions of others. He asks for their forgiveness and they grant it, and Gil asks Nigel if he can help Hal find his way home before they die. Nigel agrees to drain the world's grid power and open the rift. However, Hal refuses to let them die.
As they proceed upward in the dirigible, Hal's ring flickers but he assures the others that he's fine. Nigel warns that they can only open the rift once and then his equipment will burn out. Hal flies into position and Nigel directs his ray at the precise point in space necessary. Hal adds his ring energy and opens the rift... and then widens it so that it encompasses the planet, sweeping it into his universe. However, the power ring flickers and Hal concentrates, sending it through with one final effort and then passing out. He plummets into the planet's atmosphere and Gil flies down and carries him to safety.
Later, everyone enjoys tea and Nigel finds Kilowog. When he contacts Hal, Hal invites him to meet a few billion new friends.