The Clue of the Twisted Candle

A house in Cadogan Square, London, in which extensive alterations have been done by the Greek owner. One of the rooms is built like a safe. The walls floor and roof are made of almost indestructible reinforced concrete. The only door to the room can only be opened or closed by the owner. The single window is unreachable and there is a steel safe built into the outer wall which is in plain sight of the local policeman who patrols the street every night. Yet it is in this barred and shuttered room that the Greek is found brutally murdered.