Zanna
At the start of the novel, it seems that Zanna is going to the the protagonist and the hero, because she is the Chosen One that has been prophesied to save UnLondon. She is a student at Kilburn Comprehensive, a huge public school in London, where she is shy and doesn't smile much. She is befriended by Deeba who manages to make her laugh, and the two become best friends.
There is huge responsibility on Zanna's shoulders in UnLondon, but she is really not up to the task. Although she is The Chosen One, her skills and what the Chosen One is destined to do are not really matching up. During her first altercation with the Smog in UnLondon she breaths in polluted air, and falls ill. She returns to London having had her memories of UnLondon completely erased. She does not go back to UnLondon again.
Deeba
Deeba is a student at Kilburn Comprehensive, and is far more confident and outgoing than Zanna. She befriended her when she was a "new girl" at the school and they have been best friends ever since. Unlike Zanna, when they leave UnLondon after their first visit, Deeba's memories of the place are not erased, and consequently she cannot stop thinking about her time there. She is the perfect savior of UnLondon because in many ways she is an UnHero - she is not the stereotypical female lead, she does not have the moniker of the Chosen One to back her up, and she is thoughtful and independent rather than conforming to the way that things have traditionally always been done. Deeba is a team player which is ultimately what enables her to defeat the Smog in the first place. Because she was not prophesied to be the Shwazzy she is given the title the UnChosen One instead.
Hemi
Hemi is considered to be a ghost by Brokenbroll, but only because he is trying to scare the girls away from him and any help he might give them. In actual fact he is part-living, part-ghost. His parents were a live UnLondoner, and a dead Londoner. This means that he is able to communicate with both the living and the dead , something that regular ghosts cannot do. He is spitefully called a "half breed" by both the living and the dead and consequently has trouble fitting in anywhere.
Benjamin Unstible
Is he alive? Is he dead? Nobody is really quite sure until the end stages of the book. Unstible was killed by the Smog but brought back to life so that the Smog could possess him. However, whilst re-animated he managed to invent a formula that made umbrellas smog-resistant.
Brokenbroll
The keeper of the broken umbrellas - or UnBrellas - Brokenbroll positions himself as a friend and an ally when the girls first meet him, but when Deeba returns to UnLondon she discovers that he has been in cahoots with the Smog all along. He controls all of the umbrellas in UnLondon and makes sure that they are no help in protecting UnLondoners from the Smog. He is a scientist and really very clever but he uses his intelligence for evil and not for good.
The Smog
The Smog is a living cloud of radioactive pollution that was created by the over-use of chemicals by the citizens of London. It hungers after knowledge and information and also greedily consumes new gases and chemical fumes whenever the opportunity arises. In the nineteen fifties, the Smog tried to attack London but was seen off by the Klinneract - a mis-heard version of the Clean Air Act of 1956. It has brought Brokenbroll on board so that together they can take over UnLondon.
The Book
The Book is a volume of prophecies that almost always turn out to be wrong. It is the Mrs Malaprop of prophecy tomes. The Book befriends Deeba but is suspicious of Hemi. Nonetheless he works with them and helps to defeat the Smog by suggesting that they use the UnGun.
