When The Broken Sun, an ancient artefact said to lead to the lost city of Atlantis, is stolen from the British Museum, Jack, Scarlet and Mr Doyle embark on a hunt across Europe to find it.
But just as the artefact is within reach, their beloved secretary is mysteriously poisoned.
In their race against time to find the antidote, the team uncovers a deadly plan, to attack the Houses of Parliament.
Though no one has banked on another shocking discovery - that Mr Doyle's long-dead son may still be alive...