When Nell Villiers policeman husband vanishes on a routine case, her life is wrecked. Placed under protection by Inspector Lestrade, Nell is ripped from her old life and her own secret investigations. Instead, she must live as the widowed Mrs Hudson in a safe house: 221B Baker Street.

Two years later, with the case still unsolved, Nell vows to defy Lestrade and use her skills to discover what happened. She takes a lodger to cover her tracks; a young man called Sherlock Holmes. Before long, he is working on her case and Nell is assisting him.

But as Nell delves into her past she raises ghosts whom one person would rather keep buried. Will she face danger, and risk her new life in the process?