A pulpy, atmospheric tale that follows Mycroft Holmes, the taciturn mastermind of the Diogenes Club, as he is pulled into a labyrinthine conspiracy blending espionage, occult horror, and alternate-history intrigue; tasked by the British establishment to unravel a series of uncanny crimes and an escalating plot that threatens the nation, he navigates rival agents, arcane cults, and bizarre sciences, deploying icy logic and bureaucratic ruthlessness in a witty pastiche of detective and spy fiction.