<p>The explosion was heard twenty miles away. It killed boatmen and wrecked the exotic villa of Lawrence Alma-Tadema, the fashionable St John's Wood artist. But what caused the 1874 Regent's Park explosion? Fenian bombs? Sabotage by rival railways or other firms? Or was it something personal? And whose was the other body found in the canal? An artist's model? The missing King's Cross barmaid? Or another victim of the so-called Thames murderer? As...