This is the story of Efren, a young ratling born into the Court of Tasting, in the rat Kingdom below the streets; and Dogboy, a 13 year-old boy abandoned and living wild.

The Kingdom is in turmoil after the death of the old king, murdered by a human scientist, Dr Henry Ross-Gibbon. Ross-Gibbon is obsessed by the annihilation of all rats, and uses Dogboy to help him catch his samples. In this time of uncertainty and outright war against the world above, a new regime emerges from the courts of Spies and Translators. But Efren's fate does not rest with the relative safety of the world below. For the world above is about to make a decisive and devastating attack on the Kingdom, leaving Efren exiled, the citizens scattered, the Twyning dead. And there cannot be a Kingdom, without a rat to rule.

Hurt and alone, Efren escapes to the world above, where he finds shelter with Dogboy and Caz, a runaway 11 year-old girl. But the children discover an unlikely ability, they can talk to Efren, and he can talk to them...