It is the early spring of 2016 and Queen Elizabeth is at Windsor Castle in advance of her 90th birthday celebrations. But the preparations are interrupted when a guest is found dead in one of the Castle bedrooms. The scene suggests the young Russian pianist strangled himself, but a badly tied knot leads MI5 to suspect foul play was involved. The Queen leaves the investigation to the professionals--until their suspicions point them in the wrong direction. As she carries out her royal duties with her usual aplomb, no one in the Royal Household, the government, or the public knows that the resolute Elizabeth will use her keen eye, quick mind, and steady nerve to bring a murderer to justice.