When Eliza Scarlett's father dies suddenly, she's faced with a stark choice. Accept the fact she is now penniless or take on and run her dad's detective business, but can she succeed against all the odds in this male-dominated world?

As London's only female detective, Eliza is struggling to get work. Desperate for money, she takes a seemingly impossible case; proving the innocence of a man found at a murder scene with a bloodied knife in his hand who has pleaded guilty.

Times are turbulent in 1880s London with social unrest rife across the city. Scotland Yard have their eye on many potentially disruptive gangs and political groups and Eliza is hired by Duke to go undercover and infiltrate one such organisation - a women's suffrage group campaigning for the vote.

The Victorians were obsessed with death and the afterlife and one curious custom had people paying a photographer to capture the image of a relative who had recently passed away. Eliza finds herself contacted by one such 'Death Photographer', James Henderson, who is receiving bizarre and threatening messages from beyond the grave. Decidedly spooked, he turns to the Scarlet Detective Agency for help.

When recently investigating a mystery rooted in Victorian London's fascination with the dead, Eliza Scarlet had discovered her own recently deceased father's lost casebook. With Henry Scarlet's book throwing up some puzzling questions, Eliza looks more closely into how he died. Was it really natural causes as was determined at the time? The final entry in the casebook takes Eliza to an abandoned prison on the outskirts of London. She and Duke investigate what seems like an empty building, but they soon discover that it is the hideout for a criminal gang. But how is this gang linked to Henry Scarlet? With her resolve to solve this most personal of cases growing, is Eliza really ready for the terrible secret that is about to be uncovered?

Eliza is desperately trying to get to the bottom of the death of her detective father, Henry. Presumed to have died from a heart attack, Eliza has discovered things aren't what they seem and, with time running out, she has to piece together a perplexing puzzle. Adding to the mystery is the fact that Moses, the notorious Jamaican crook she's often turned to for help, appears to be involved somehow. He has lots of criminal connections, which surely make him a prime suspect. But, as she goes deeper into the investigation, she discovers that the world isn't so black and white - who is on the right side of the law and who is on the wrong side isn't always as it appears. Of all the cases she's investigated since taking over her father's detective business, this is the one with the highest stakes!