The curse of Macbeth played its part in one of the bloodiest ever riots in the United States. On 10 May 1849 US militia killed 23 and wounded over a hundred people at the Astor Place Opera House in New York. Was this just the unhappy climax of a long-standing feud between two actors? Tim Pigott-Smith traces the events, examining the tensions between nations and the antagonisms between classes in a city ripe for reform. Producer Merilyn Harris