Holmes and Watson were summoned to the manor house of the Barclay-Alston estate. Sir Wilfred Barclay-Alston had been found dead in his bed while his young and beautiful wife Edwina was out of town. The family physician had been called and declared him dead of natural causes but the late lord's nephew Philip suspected foul play. 

The pair arrived and began interviewing all of the staff. The maid and butler heard and saw nothing out of the ordinary and the gardener had been watching television in his cottage before going to bed and had seen no horses or carriages come or go.

When they talked to the physician, who had been a guest of the manor the night of the death, he showed them the body of Sir Wilfred. The elderly man had several lingering health problems, so death from one of those was not unexpected.

Holmes and Watson insisted on conducting a thorough examination of the corpse themselves. Holmes peered into the eyes and sniffed at the mouth of the late lord and pondered a moment. "Watson," he announced, "Double check the body, looking for a puncture wound somewhere. Probably in a fleshy place near a large muscle."

Watson undertook the additional examination, borrowing Holmes' magnifying glass to look everywhere. "Aha!" he exclaimed. "Here, Holmes! I've found it!"

Holmes hurried over. Watson had turned the body over and pointed to a small red pinprick on the left buttock of Lord Barclay-Alston. "Here, just on the side. There is a small hole. And here on his nightshirt is a tiny spot of blood where he was injected with something!"

The pair of them moved the body off the bed and after a search found a syringe which had been cleverly placed under the mattress so that when the old man climbed into his usual spot it would pierce the gluteal muscle, his weight depressing the plunger. Holmes removed the syringe and, sniffing the empty barrel, announced, "Curare! Just as I had suspected. It's evident the Lady Edwina and the doctor were having an affair and did Lord Wilfred in while she was away to deflect suspicion."

Watson goggled at his friend. "How did you ever deduce that I should check for a puncture wound?" he inquired.

"It was elementary, Watson. The lord showed all the signs of having been fatally affected by a nerve toxin. I didn't detect any residue on his breath. The physician mentioned having spent some time as a missionary in South America, so he would have known about curare. And when you found Lord Wilfred had been punctured in the backside it confirmed that it was a case of arse nicked poisoning."