A young woman is found dead in Richmond Park. It turns out that the deceased is the wife of wealthy businessman Conrad Sanders. Inspector Wolfford immediately requests Sherlock Holmes and Dr Watson's assistance at the start of the investigation. It quickly becomes clear that the murder could only have been committed by a left-handed person. Unfortunately, there are three suspects to choose from: Conrad Sanders himself, his brother Stuart, and the riding instructor Rick Hunter, who had been having a passionate affair with the victim. There are clues and speculation, but proof is lacking. Then Holmes has a brilliant idea... and the trap snaps shut!