After his fiancée, Edith Presbury, sees an intruder outside her 2nd floor bedroom in the middle of the night, Jack Bennett seeks the services of Sherlock Holmes. When Holmes and Watson arrive at the Presbury house, they are confronted and evicted by Ms Presbury's father (who is also Mr Bennett's employer), the famous natural scientist Professor Presbury.
An unusual episode of Sherlock Holmes, especially as regards the background and revelation. While quite fantastical, some of the mystery of the 2nd floor intruder is revealed in the opening scene. Fortunately this doesn't completely explain the goings-on at the Presbury house so there is still quite a fair bit of mystery to solve.
The left-field nature of the conclusion does feel more like sci fi than a detective drama in the end, making for a clumsy, contrived sort of feel to proceedings. Nevertheless it's interesting enough.