Book Four of Series One.Fresh from their adventures on Mercury, Nathanial Stone and his ward, Annabelle Somerset, are limping through the aether in a dilapidated flyer when they unwittingly stumble upon a heliograph station in solar orbit between Earth and Mars.Now in the sinister clutches of Dr Henry van den Bosch, a hulking nightmare of a man with a penchant for destroying those who cross him, Nathanial must race against time to prevent the station from falling into a massive aether vortex or risk van den Bosch's wrath.But unseen forces hold sway on Peregrine Station, and before the two can even settle in, an attempt is made on Nathanial's life. Annabelle investigates, and in doing so sets off a chain of events that could destroy the station before it ever reaches the vortex.