London has fallen, consumed by the flames of the Crimson Affliction. For Sherlock Holmes and Dr. Watson, escape aboard a Navy patrol boat offers not peace, but a grim new reality within the fortified walls of RNAS Solent – 'Project Nightingale'. Amidst ration queues, military drills, and the pervasive fear gripping the island refuge, Holmes's formidable intellect finds a new, terrifying puzzle: the plague itself.

But this is no mere biological anomaly. Sabotage plagues Holmes's makeshift lab, vital research is compromised, and whispers of unnatural virulence hint at a truth far darker than random mutation. While battling bureaucratic resistance and the deep suspicions of base commander Davies, Holmes, aided by the brilliant but haunted Dr. Elara Vance, uncovers fragmented clues pointing towards a horrifying possibility: the Crimson Affliction may be an engineered nightmare, a weapon unleashed.

As mutated strains wash ashore and a terrifying 'Crimson Chorus' signals coordinated attacks, Holmes must race against time, not only to find a defense against the evolving horde besieging their sanctuary, but also to expose a conspiracy reaching into the highest echelons of surviving command – a conspiracy desperate to bury its monstrous secret, Project Hemlock, even if it means sacrificing the last vestiges of civilization. The game is afoot once more, but the board is a dying world, and the stakes are humanity's very survival.