The Hearth Clue

I slipped down the carved desk leg at dawn, guided by that sepia blueprint from the drawer. Across the hardwood expanse, the brick fireplace waited like a grand architectural puzzle. Kneeling on the cool flagstone hearth, I brushed aside a stray flake of charcoal and spotted a faint seam in the cast-iron fireback. Tapping the iron with the small brass key I carried, a dull hollow chime echoed back into the chimney. There really is a hidden chamber behind the grate, wouldn't you say?