It is 1896. In an alternative history where Babbage’s difference engines have become commonplace Captain Charles Maddox, wrongly convicted of a murder and exiled to military service in Canada eight years ago to avoid prosecution, is illegally returning to Britain to visit his dying father.

Recognised by an old acquaintance connected to the murder, Maddox is challenged to a duel and, returning to an old haunt, is caught up in a raid by the paramilitary Bureau of Engine Security. He is arrested, interrogated and imprisoned in a high security cell at Millbank gaol, to be held there, awaiting the death sentence he had previously avoided.

Instead, he is rescued by a covert agency called the Map Room.  Maddox is given the choice of taking his chances with the Bureau or joining the Map Room as an agent and helping them uncover a possible conspiracy surrounding the 1888 Ripper murders. Seeing little choice, Maddox accepts the offer.  Under the codename Sterling, he joins the team of fellow agents Church and Green, controller Collier and in-house mechanical computer expert, or ‘tapper’, Patience. Overseeing them all is the well-to-do, well-connected and frighteningly well-informed head of the Map room, whom Maddox knows only as Milady.

With help from the Map Room team, Maddox (now Agent Sterling) and Church’s investigation takes them from a tour of the Ripper murder sites to an upmarket teaching hospital, and from a criminal fixer in the East End of London to the fringes of Blackpool nightlife.

Along the way Church and Sterling uncover a years-old and closely-guarded conspiracy deep within the Bureau, and one that its members will go to any lengths to protect. Success depends on the two of them quickly forging a successful partnership as agents and following the trail wherever, and to whomever, it leads. In doing so they can put the Ripper murders and the conspiracy surrounding them to rest once and for all.