El nudo Windsor

It's early spring 2016 at Windsor Castle, where Elizabeth II finalizes the preparations for her 90th anniversary celebrations over a morning cup of tea. But the festive atmosphere is suddenly cut short when one of her guests is found dead in one of the dormitories of the residence. Everything seems to indicate that the young Russian pianist has hanged himself, but a badly tied knot leads MI5 to suspect that there is a cat locked up. The queen leaves the investigation in the hands of the professionals, until the investigations point towards her faithful servants and she decides to take action on the matter.