This second Sally Lockhart mystery takes place in late 1878, six years after the events of The Ruby in the Smoke.

The seance involves the table shaking from side to side and objects being thrown across the room; the medium (a Mrs. Nellie Budd) also has trance during which she says things that connect to a mysterious business tied up to Anglo-Baltic called North Star.

Sally suspects that Bellman has manufactured Anglo-Baltic's collapse to fund North Star; she believes him to be very vicious.

Frederick and Charles also come across Lord Wytham and his ethereally beautiful daughter Lady Mary.

Sally visits Bellmann and orders him to pay her Miss Walsh's lost money but he refuses.

Frightened, she tells them where Mackinnon will be performing but Frederick, Sally and Jim are able to save him by allowing him to get away from that venue so he is not harmed.

He tells her that he is Nellie Budd's son by Lord Wytham but then runs away from her (as well as the henchmen) before she can find out more.

Meanwhile, Sally finds out that North Star is a weapons company that plans to build a massive "Steam Gun" capable of shooting thousands of bullets at once.

Frederick learns how the Steam Gun works and comes across Nellie's sister Jessie in the north of England.

Frederick learns from a hostel owner that Mackinnon is married to Lady Mary Wytham.

Jim and Frederick fight, with a moment of instrumental help from Mackinnon, against the henchmen, eventually knocking them out.

Everyone climbs out of the window (Jim falls and breaks his leg) apart from Isabel who refuses to leave her room.

Frederick climbs back up to save her but she refuses to move and the ceiling collapses, killing them both.

Back in London, despite Jim's broken leg, he manages to walk to where Mackinnon is staying.

Mackinnon sees where Sally is using his psychic powers and Jim makes him come to the North Star headquarters.

Sally tells Mackinnon to wait before agreeing to marry Bellmann in exchange for the money Miss Walsh lost from the collapse of Anglo-Baltic.

Bellmann gives the money to Sally who tells Mackinnon to take it to Miss Walsh.

Bellmann's death is reported as a tragic accident; Miss Walsh gets her money and insists in investing it in Garland & Lockhart (the photography firm Sally helped set up); it transpires that Jim will walk with a limp for the rest of his life thanks to his efforts to rescue Sally when his leg was broken; Nellie Budd recovers and decides to go back to the north with Jessie; and Mackinnon and Lady Mary leave England to go to America.

In the spring of the next year, Charles shows Sally, Webster and Jim a possible new location for Garland & Lockhart after the fire.

A BBC TV movie adaptation starring Billie Piper as Sally Lockhart, JJ Feild as Fred Garland, Jared Harris as Axel Bellmann and Matt Smith as Jim Taylor.