Geometric diamond tattoo across upper back

Ada Okafor came to Harrow Point the winter the new cladding went on. Every flat got fresh windows, and the men stacked the old ones against the bin store like headstones. Ada took one home on her shoulder. Nobody knew why until she pinned a sheet of graph paper to her kitchen wall and started drawing with a ruler she'd nicked from the school next door. She drew a diamond, solid as a coal, then a triangle beneath it, then lines fanning out from the point like spokes on a bicycle wheel. Wherever two lines crossed she put a dot, and the dots kept going until the whole sheet hummed.

Ask anyone on the eleventh floor what the diamond was and they'll tell you it's the shape of the stairwell seen from the roof, which is nonsense. It was the shape of the light. At five each evening the sun slid between the two towers and came through the bare stairwell glass in one hard wedge, and it landed on the wall exactly where her black diamond was painted. She'd stand in it with her coat still on, not moving. Then one February the sun found a gap in the flats opposite and threw a small bright disc across the lift mirror, and Ada laughed so loudly the caretaker came up the stairs to check she hadn't fallen through the floor.

They knocked the block down in the spring. Ada had gone by then, and she never saw the dust settle. Somebody posted her a photograph of the rubble, and in the top corner, where the light had caught it, there was a little sun the colour of stewed tea. That's how I know the story's true. Right, here's the landing. Mind the step where the lino gives up.