The Earth is in another ice age and civilisation is restarting in a future so distant that the only traces left of our time are a few precious shards of glass. When the seas rose and the earth froze, much knowledge was lost, and in this new ice world a little science goes a long way.
Hexult is a remote group of troubled islands in a vast ice ocean, separated by the treacherous Vajra Crevasse. Aulf is the young mail man, sailing between the islands, delivering the mail with Ithe help of Ingar, a half wild orphan girl. The story begins as they discover a wrecked boat on the open ice and rescue and befriend a mysterious pair of fifteen year old twins, Jacob and Elya.
The strangers’ superior knowledge of science and technology means Elya and Jacob are soon regarded by the people of Hexult as magicians. This annoys the islands’ resident wizard, Gabriel, who pursues devious ways to undermine the twins’ credibility. Jacob and Elya suggest building signal towers to improve communication and help mend the troubled relationships between the islands – wizard towers as they soon become known. To fund the project, the twins recruit Jeremiah Grimwold, a blacksmith, to produce ‘magical’ firelighters from a metal they call steel. These 'wizard strikers' soon revolutionise the islanders lives.
Problems arise for the twins in the form of a prophecy which supposedly foretells of their coming, and links Jacob with hope and Elya with treachery. Elya soon finds herself rejected by the islanders, and relationships with her brother and her new friends become strained.
Pursued by raiders, the four friends have a close encounter with the Crevasse which leaves them marooned on a tiny island, until they are rescued by a young woman and her sled dogs. Back on the main islands, Jacob makes a success of the towers, despite Gabriel trying to steal the glory of the towers for himself, but Elya becomes the target of the islanders’ superstitious prejudice and she is forced to run from a vengeful mob, captured by raiders, and eventually rescued by Isambard, the enigmatic chieftain of the remote and wild island of Thorland, a place regarded with hostile suspicion by the rest of Hexult.
Jacob, Aulf and Ingar, unaware of Elya’s fate, grieve her loss, but, as time passes, continue building wizard towers on the other islands, and Jacob proposes the islands hold a joint ice fair. An ice tower is constructed on the open ice in preparation and great excitement surrounds the fair. Then Jacob receives an unexpected message via the tower – from Elya, who has built a tower on distant Thorland. They arrange to reunite at the fair.
The ice fair gets off to a good start, but disaster strikes as the event is sabotaged by a raider attack, set up by Gabriel. All seems lost until a fleet of Thorland boats unexpectedly appears on the horizon. Elya has persuaded the maligned Thorlanders to make peace with the other islands and brought them to the fair. A battle ensues and Elya's life hangs in the balance, but the Thorlanders win the day and tragedy is narrowly averted.
Elya’s return is met with hostility from the other islanders and she is accused of using dark magic to the detriment of the islands. Only Isambard’s intervention saves her, and she is finally reunited with Jacob, Aulf and Ingar. The first book ends as the twins lay aside the ghosts of the past and look towards their future.