The Green Storm has legions of soldiers and undead cyborg Stalkers, fighter airships called "Murasaki Fox Spirits" and "Zhang Chen Hawkmoths", which are vast air destroyers and carriers.

The title is probably a reference to the words of the Stalker Fang in Predator's Gold: "...and then we shall release a storm which will rid this world of [the Tractionists'] infernal devices happily ever after forever.

When she sneaks out one night Wren encounters three Lost Boys, Remora, Fishcake and their older leader Gargle; who have come to Anchorage in search of a mysterious Rasmussen family artifact named the Tin Book.

The Book, bearing the insignia of the President of the United States of America, contains the activation codes for the final remaining orbital weapons left over from the Sixty Minute War; potentially with firepower far greater than that of MEDUSA, which destroyed the Traction City of London in Mortal Engines.

After meeting former Lost Boy now Anchorage resident Caul, who refuses to help him, Gargle persuades Wren to retrieve the Tin Book for him and to join them on their journeys around the world.

Wren begins her mission by asking the now-adult margravine Freya Rasmussen, knowing that the Book is in the palace's library.

When Wren reports to Gargle he tells her that Nimrod Pennyroyal's book about the time he spent in Anchorage has revealed the Lost Boys' existence to the raft cities that they previously robbed.

En route to the sunken city, Fishcake receives a communication from the raft resort of Brighton, claiming that the parents of kidnapped Lost Boys have united to track down their missing children.

Arriving at the raft-city pleasure resort, the pair's limpet is captured and the two are taken in as slaves, the communication being a ruse to stop the Lost Boys.

Shkin interrogates Fishcake, who reveals the location of Grimsby, prompting Brighton to change course and destroy it with depth charges.

Fang has the Green Storm armies extend their borders via bombing and destroying Traction Cities, starting a war with the Traktionstadtsgesellschaft.

Hester discovers Pennyroyal's corrupted version of the events of Predator's Gold, including that she sold Anchorage to Arkangel and the renamed exhibited Jenny Haniver.

Shkin plans to use Tom and Wren to expose Pennyroyal as a fraud and retrieve the Tin Book to sell off to the highest bidder.

Told by Tom via a note that he was going to the Pepperpot, Shkin's base of operations, Hester plans to release the slaves inside to create a panic.

Destroying it and taking the Tin Book, the pair discover that Cloud 9 has been set adrift and that a Green Storm airship is heading toward Brighton.

Secretly disgusted by Fang's actions in the war and wasting men, Naga commends Zero for orchestrating the Stalker's demise and takes control of the Green Storm.

Pennyroyal tells Wren that Hester sold Anchorage to Arkangel, one of the few elements of his book that was true, but she doesn't believe him.

Tom, Wren, Theo and Pennyroyal escape in the Jenny Haniver as Cloud 9 finally collapses onto the African shore.