Her Imperial Majesty Queen Victoria still rules New England and her American Possessions; the Royal Navy rules the skies with its mighty Airships; and Earth still turns on God's great brass gears of Heaven as it makes its orderly passage round the Lamp of the Sun from Midnight to Midnight and Year to Year.

In the town of New Haven, a Clockmaker's young apprentice is visited at midnight by a a brass Angel, and told that he, and he alone, can find the Key Perilous to rewind the Mainspring of Earth. If he does not, the planet will wind down, and life will cease.