In the fifth book in the Castle series, Steph Swainston returns to her uniquely imagined fantasy world.

Fifteen years after the last devastating Insect attack, the immortal Circle is finally ready to launch an offensive against their implacable enemies. This time they have a new weapon gunpowder. Hopes are high.

But the Circle's plans are threatened when the vital barrels of gunpowder go missing. Jant, the Circle's winged messenger, is tasked to investigate. Soon it becomes clear that the theft is part of a deadly conspiracy . . . and Jant and his friends are among the targets.

As tensions rise, Jant races to foil the conspirators. Can he expose them in time or will the crisis blow the Fourlands apart?