Tobias lifts his hand slowly and the spider-silk thread catches the lantern-light, glimmering faint violet at its far end — the colour barely there, like starlight in water. He follows the line with his eyes: up the copper lantern's chain, then sideways across the crumbling wall to where the mortar has fallen away entirely, leaving a gap the width of his fist. A violet pulse breathes from inside it. Slow as a heartbeat. Warm as the cobblestones. He steps forward and kneels. Tucked into the gap is a tiny alcove worn hollow by rain, and inside it three more silk threads are coiled around a second iron hook — the glow throbbing steadily between them like a caught firefly. Beside the hook, pressed into a film of old mortar dust, is a footprint the size of his thumbnail. It points not toward the door. It points straight up the wall.