For Nathanial Stone and Annabelle Somerset, the most harrowing journey has only just begun!

At long last, Nathanial and Annabelle are back on Earth, but the reception is hardly what they hoped for–Nathanial locked up in Chatham Convict Prison, Annabelle and her uncle Cyrus Grant held in the Tower of London: the charge–treason!

Someone high up in the British government is putting pressure on them for mysterious reasons. But when the Austro-Hungarian ambassador to Britain is assassinated in a gunpowder plot, which would have made Guy Fawkes smile, events spin out of everyone's control.

The clock is ticking down on the arrival of the new Austrian ambassador, and on an assassination plot which aims to cut the heart out of the British monarchy and government. The race to thwart the conspirators will take Nathanial, Annabelle, and George Bedford through the heart of Whitechapel at night, to gunpowder barges anchored in the Thames, to seedy boarding houses attacked by infernal clockwork devices, and finally to the dizzy heights of a zeppelin docking gantry packed with explosives and where a single spark will mean extinction for all.