In 1930s Liverpool, England when a wealthy widow's life is put in danger and a mysterious amulet holds the key to the culprit, Jessie Harper and George Jenkins of the Dale Street Private Investigations Agency must use their wits and the help of Khan, a talking cat with magical powers, to unravel the mystery and save her.

Jessie Harper and George Jenkins are partners in the Dale Street Private Investigations Agency, a small but successful business that specialises in solving crimes that the police can't or won't handle usually because of paranormal connections to the crimes. They are hired by Lady Evelyn Montague, a wealthy and eccentric widow who lives in a mansion on the outskirts of Liverpool.

She claims that someone is trying to kill her and that she has received several threatening letters. Later, a guest of hers is murdereed.

With the help of Khan, Jessie's feline companion. who is a talking cat with magical powers, they must unravel the mystery before the killer strikes again. Along the way, they must deal with a host of suspects, including Lady Evelyn's greedy relatives, her shady lawyer, her mysterious maid, and her eccentric friends. They will also have to face their own feelings for each other, which they have been hiding for a long time. With help from Detective Sergeant Bill Roberts of the Liverpool City Police and using their wits, Jessie and George must find out who is behind the plot and what is the secret of the mysterious amulet before it's too late.