The novel is set in the Fourlands, a country in danger of being overrun by large hostile Insects, and follows the exploits of Jant, also called "the Messenger" or "Comet".

As a half-breed of two humanoid species Jant is the only person who can fly, which makes him an indispensable part of the Emperor's Circle of about 50 immortals, an elite group of (mostly) warriors who do not age (but, despite the name, are capable of being killed).

A young soldier, Wrenn, challenges the immortal Swordsman Gio Serein and defeats him to earn his place in the Circle.

Along with Lightning the Archer and Jant the Messenger, Wrenn is chosen to accompany the Sailor Mist on her voyage to the newly discovered island of Tris, three months' journey from the Fourlands.

With the stress of the voyage and worries of his wife's infidelity, Jant begins to use the drug scolopendium again, which allows him access to the bizarre alternate world known as the Shift.

Wrenn, armed only with a rapier, is unable to stop it; the Insect kills several Trisians and escapes into the sewers.