X + Y = K is the final, astonishing work by the late Ciaran Carson - an electrifying fusion of memoir, ghost story, and speculative fiction that pushes his lifelong preoccupations with memory, time, and perception into audacious new territory. Moving between Belfast and London, the novel traces the fractured consciousness of Kilpatrick, a man haunted by migraine visions, childhood trauma, and the spectral machinery of history. As séances, scientific experiments, and art-historical meditations bleed into one another, the boundaries between worlds grow porous: tables levitate, cities shimmer like palimpsests, and the dead return in flickers of light. Carson's trademark blend of forensic detail and lyrical expansiveness animates a narrative where parallel realities overlap, where surveillance and spiritualism mirror each other, and where every object - painting, watch, typewriter - carries its hidden aura. A profound meditation on vulnerability, doubleness, and the stories we invent to survive, X + Y = K is Carson's final, radiant act of imagination.