The Charwoman's Shadow by Lord Dunsany

"So it does not grow," said Ramon Alonzo bitterly.

He was all alone on the hill and the girls had fled. Alone with a mere strip of gloom; a thing refused by the charwoman. So this was the shadow he had received so confidently, believing he had obtained from magic something without payment. A mere patch of darkness that neither dwindled nor grew. In a flash his memory went back to the suspicion he had suddenly had on the stair, and recalled how the shade of the trees in the heat of the day had hidden the evil secret a little longer. He remembered how two evenings ago it had seemed not so late as it was; that was his lying shadow. But he no longer thought of it as a shadow at all; it was mere art, and the Black Art at that. It counterfeited what his own shadow had been in the middle of that fatal afternoon, and could no more grow than shadows in pictures grow.