The Brown Suit - Agatha Christie

Anne has come to London in search of adventure.

And I found her on the spot... on the tube platform at Hyde Park station. There, the skinny man retreated in panic, only to fall onto the train tracks and die of electrocution.

The police say the death was an accident, but Anne isn't convinced. And anyway: who was the man in the brown suit who bent over the corpse to examine it? And what is that strange message that fell from him while he was fleeing?