Sherlock Holmes and Doctor Watson are visited by a young lady of 30 with a face like a hunted animal. Fear, it seems, causes her to constantly shiver. But her horror lies in the fact that her fears are so vague. Two years ago, in the small hours of the morning, a low whistle was heard in their ancestral home. It was then that her sister suddenly died. Now she lives in the same room her sister vacated, and last night, the whistle sounded again.