When Murder at Archly Manor opens, it's 1923 in London and Olive Belgrave is in search of a job that's as unconventional as she is. Upon being presented with suspicious information about her cousin's mysterious fiancé Alfred, Olive jumps on the opportunity to conduct a background investigation about him. Expecting to find conclusive answers, Olive instead finds questions and finds herself as the head detective of her first case. Then when a blue-blooded murder occurs at a glamourous aristocratic party, it's up to Olive to uncover the truth amidst all the twists and turns overcomplicated by London high society.