The story is based on an Indian urban legend that tells of a Muslim who was forced to have his arm amputated after an accident, and died a few months later, but after death became a ghost and began wandering about in search of his limb.
The main character is a doctor who has had a long spell of service in India. Once when he was posted at Peshawur, then a main city of undivided Punjab (hence a part of India), he had to attend a poor tribal man whose one hand was in such a bad state that only way to save his life was to amputate it. The man, being Muslim, was fiercely against this un-Islamic way, but since it was a question of life and death he had to compromise and let the Englishman cut his hand. The doctor had a hobby - collecting such things as cut limbs, discarded organs from living and dead humans, so he put the "brown hand" in a chemical solution to prevent decay, and took it back to Wiltshire when he retired. Then one night he was awakened by something pulling his clothes: it was the ghost of his old patient. From then onwards the ghost haunted his lab, looking for his hand but failing to find it since it had been misplaced long ago. At the end the doctor is saved by the protagonist who arranges another amputated hand (from a "lascar" who has had an accident). The ghost is tricked into thinking this is its hand, and vanishes forever (with his beloved hand, of course), leaving the doctor to live in peace. The doctor rewards the protagonist by making him his heir.