There is a terrible tragedy in the family of high-ranking London politician Sir Basil Muidor. In the middle of the night, someone killed his beloved daughter Octavia, stabbing him in the chest in her own bedroom. An unheard of crime! Therefore, the most brilliant detective of the Metropolitan Police, William Monk, was assigned to investigate him. At first, the most obvious version of what happened seemed to be the penetration of a robber into the house, who inadvertently woke Octavia up and was forced to kill her. But then Monk irrefutably proved that no one could get into the house from the outside. And therefore, this was the work of one of the household members - servants or relatives. The matter immediately took on a special turn...