Metropolitan is set in an unnamed world covered in a single enormous city, where the main source of power is plasm, a mysterious energy formed from geometric patterns such as the arrangement of buildings. Plasm is used in a way that sits somewhere between magic and technology - it powers the lights and the trains, but individuals can also use it for astral projection, creating energy, healing, killing and the like. This makes for an intriguing world, especially when you find that it is sealed up by a mysterious Shield in the atmosphere, which prevents anyone getting out.
Aiah, the heroine, is a minor functionary for the Plasm Authority, a company controlling plasm in her metropolis. She's also a member of a displaced ethnic minority who are mistrusted in the city, although Aiah tries to pretend she's above all that. This, and other aspects of the world's history, aren't always explained very fully, despite being potentially interesting.
While searching for the cause of a disaster, Aiah finds an enormous source of plasm beneath a building and rather than reporting it, decides to sell it to solve her domestic money troubles. She ends up offering it to Constantine, a powerful mage in exile with revolutionary views, despite knowing that he will undoubtedly use it for some dangerous political stunt.
Metropolitan is very well written, brimming with ideas, and the main characters are well-drawn. But the end, as Aiah gets drawn deeper into Constantine's plans, is abrupt and doesn't resolve very much, which makes for an ultimately frustrating book.