Follows an elite team of detectives as they investigate murders in London.

Set in 1850s London, Miss Eliza Scarlet continues her father's detective agency after his death, investigating crime with the help of a reluctant family friend, Detective Inspector William "the Duke" Wellington of Scotland Yard.

In Miss Scarlet and The Duke Season 4, Eliza has taken over the business of Nash & Sons (not that he has any sons) and things are not going entirely smoothly, although help comes from some familiar sources. Outside of work, her relationship with William 'The Duke' Wellington builds towards a looming decision that will shape both their lives.