*CUT TO THE CHASE*
This spoiler was submitted by Jeremy
The film starts with the voice of Shrike (Stephen Lang) briefly recapping a devastating event known as the Sixty Minute War, in which the Ancient Ones laid waste to the world around them, and those that remained went on to form mobile predator cities that lord over the smaller cities.
A young woman named Hester Shaw (Hera Hilmar) lives in a Bavarian mining town on wheels called Salzhaken. The much larger predator city of London goes after the smaller town via the Hunting Grounds as the wealthy and well-kept citizens of London cheer like it's a sport. The other people in the small town panic while Hester runs to the front, waiting to be absorbed by London, as she has her eyes set on London's Head of the Guild of Historians, Thaddeus Valentine (Hugo Weaving). Within a matter of moments, Salzhaken is brought inside London.
A young Apprentice Historian named Tom Natsworthy (Robert Sheehan) meets with Valentine's daughter Katherine (Leila George) as they check out London's little museum of "old tech" (smartphones, toasters, computers, etc) where Tom is sent by his boss, Chudleigh Pomeroy (Colin Salmon) to pick up some tech. They watch a brief video in which a bioweapon called MEDUSA was the cause of the destruction brought on by the Sixty Minute War. Tom is sent away by the snooping Chief Navigator named Herbert Malliphant (Andrew Lees) to London's lower level so that he can spend a moment with Kate, but she ends up accompanying Tom to his destination.
The people of Salzhaken are brought in for processing. Valentine descends to oversee things as one of the guards assaults a man from the small town. Hester gets closer to Valentine, which Tom manages to see. He calls out to Valentine to warn him, but Hester manages to stab Valentine quickly. She pulls off her scarf to reveal her facial scar and tells Valentine this is for her mother Pandora. Before she can kill Valentine, she is stopped by Tom, who chases her to a waste chute. Hester is about to jump until Tom grabs her wrist. She tells Tom to ask Valentine what he did to her mother and how he gave Hester her scar before she lets herself free of Tom's grip and falls down the chute. Valentine arrives moments after, and Tom starts to ask what Hester meant by what she said. Valentine responds by pushing Tom down the chute right before Kate and other people arrive, telling them that Tom fell in as a result of fighting Hester. Kate notices that another man, Bevis Pod (Ronan Raftery), saw the whole thing.
Hester and Tom are dropped on the outskirts of an unknown location. She picks his pockets and steals his money and knife before heading off on her own. Tom wakes up and follows Hester, thinking they should stick together, but she wants nothing to do with him. Not long after, they are spotted by scavengers and taken into a town called Scuttlebug.
Valentine speaks to London's mayor Magnus Crome (Patrick Malahide) over his plans for where to take London, but Crome has his doubts over whatever Valentine is planning, due to London living by the philosophy of Municipal Darwinism. Valentine then goes to visit his top scientist Dr. Twix (Sarah Peirse) as she is in the process of developing a weapon for Valentine. She also offers Valentine a solution for dealing with Hester.
Kate goes to find Bevis and ask what he saw. He is hesitant to say since he knows it will get him in trouble, but he finally admits to Kate that he saw her father push Tom down the chute. What's more is Bevis knows that Valentine is covering something up and is building something inside St. Paul's Cathedral, and the two try to figure out a way to get inside.
The people that take Hester and Tom in appear hospitable, but they keep the two locked in a cell. Hester then tells Tom about how she lost her mother when she was 8. Valentine was good friends with Pandora (Caren Pistorius) and always treated Hester kindly until the day that Pandora and Valentine both found something that Pandora knew Valentine wanted for his own dark purposes. They fought over it, and Valentine stabbed Pandora in front of Hester and slashed Hester's face when she tried to save her mother. Before dying, Pandora gave Hester a necklace with an eye symbol, and Hester escaped.
Valentine goes to an offshore prison to find Shrike, who is a half-cyborg/half-zombie-like creature who has a history with Hester. He is angry with her for going back on a promise she made to him, and he wants her dead. Valentine destroys the prison and lets Shrike run free to go after Hester.
Hester and Tom are brought before an auction in Rustwater where they are to be sold off as slaves. When Hester is brought up for purchase, a woman named Anna Fang (Jihae) steps out and claims she will take Hester. The auctioneer knows that Anna is a fugitive wanted by London with a price on her head, but Anna frees Hester and Tom after killing the auctioneer and several of his men. They board her aircraft, the Jenny Haniver, but they are also spotted by Shrike. He attempts to climb up and catch them as Tom is climbing the rope to the aircraft. Anna throws Hester a knife to cut Tom loose, but she throws it to Tom to cut Shrike loose. As they fly toward their next destination, Anna talks to Hester and says she knew Pandora and has been trying to find Hester since Pandora's death.
Herbert goes to find Valentine to suck up to him by informing him that a cache of old tech has been discovered, and Herbert now has Valentine's attention.
Hester explains to Tom how she knows Shrike. After running away as a child, Shrike found her and raised her for years like his own. He had always noticed how sad Hester was, and he offered a solution to make the pain go away. Shrike revealed a robotic body he made for Hester, so that she can die and be reborn as a machine with no memory of the horrors of her childhood. She almost took him up on the offer until she heard about Valentine being close, so she headed off to hunt him down and left Shrike alone and angered by her deception.
Anna brings Hester and Tom to Airhaven, where they meet her partners in the Anti-Traction League. She tells Hester that Pandora was trying to hide something from Valentine. Meanwhile, Kate and Bevis do more investigating by speaking to Pomeroy. He quietly leads them through a tunnel into the cathedral where Kate sees the large MEDUSA weapon that Valentine is holding. She also watches as he shoots down Crome when he finds the weapon himself. Anna and her team are trying to find a way to stop the weapon, as Valentine is planning to bring it to Shan Guo, a non-mobile city that was formerly China, and destroy the wall that seals it off before taking down the rest of the city. Just then, Shrike enters and starts to attack and kill Anna's teammates. Airhaven starts to go down in flames as the survivors try to escape. Shrike goes after Hester and Tom and nearly kills Tom until Hester pleads with him to leave Tom. Shrike realizes Hester is in love with Tom. He also notices he has been heavily damaged in the fight, and he is going to die for good. He releases Hester from her promise and lets her go. She tearfully leaves him, and Shrike's final thoughts are of Hester as a child. She and Tom escape with Anna and a few others.
Valentine prepares to take London toward Shan Guo. Anna talks to Governor Kwan (Kee Chan) to help launch the Anti-Tractionist fleet against London. The heroes fly toward London as they inch closer and closer to the wall. Valentine raises MEDUSA to fire the first powerful blast against the wall. Kate sees what kind of man her father truly is, and she refuses to side with him. Many of Anna's teammates are shot down and killed as another blast hits the wall. Hester and Anna manage to make it to London and head to St. Paul's. Hester finds that her mother's necklace holds the kill drive for MEDUSA. Valentine and Anna fight as Hester goes to shut down MEDUSA before the final blast can fully take the wall down. Valentine fatally impales Anna, but she lives long enough to see MEDUSA shut down.
Valentine still plans to ram London into the wall at the cost of millions of lives. Kate tries to stop London's engine, but it won't budge. Tom flies the Jenny Haniver toward the engine to blast it to bits, causing London to slow down. Valentine tries to get away on his own aircraft until Hester pursues him. He reveals to her that he is her father, having been in love with Pandora before her death. When Hester has a chance to kill Valentine, she chooses not to. She hops on the Jenny Haniver with Tom before he fires a blast at Valentine's craft, sending it crashing to the ground. Valentine survives, but only long enough to see that London's tracks are about to crush him.
Kate leads the Londoners to the top of Shan Guo's wall where she peacefully greets Kwan, and he accepts them in for sanctuary. As the sun rises, Hester and Tom embrace as they take the Jenny Haniver to travel the world.