The novel opens with a midnight visitation: Hethor Jacques, a young clockmaker's apprentice, finds himself charged by the angel Gabriel to seek out the Key Perilous and to wind the Mainspring of the world. After a couple of false starts, Hethor manages to get himself out of New Haven and on the road to Boston where he hopes to set his problem at the feet of those in power. But instead of being able to pass on his quest, he becomes involved in a series of picaresque episodes — including being imprisoned, press-ganged, and being shipped out to the equator aboard a military airship — all of which chance to bring him closer to his goal.
Although Mainspring is ostensibly the story of Hethor's quest, the real star is Lake's bizarre but consistent clockwork universe. For Hethor's Earth is divided into two hemispheres by a great brass wall a hundred miles hight that engages with the cogwheels that move the planet along its orbital track, driven by the power of the Mainspring transmitted through complex internal machinery that Hethor alone seems to have the power to hear and, as time goes on, influence. And these changes have impacted the physical, religious and social development of the world. Sailors navigating according to the celestial brasswork; the symbol of Christianity is the horofix, with clockmaking possessing potentially blasphemous connotations; and with Britain restricted to a single hemisphere, the Americas have remained part of an Empire that is now vying with China for power and territory.
An enjoyable novel with some wonderful world-building that reminds me of Adam Roberts On, whilst lacking the bleak absurdity of Roberts' strange Earth.