The Man in the Brown Suit: Agatha Christie

Pretty, young Anne Beddingfield has come to London looking for adventure. But adventure finds her when a strange-smelling man falls off an Underground platform and is electrocuted on the rails.
The police verdict is accidental death. But who was the man in the brown suit who examined the body before running away? Armed with only one cryptic clue, Anne is determined to track him down and bring the mysterious killer to justice.