There have been many biographies of Stalin, but the court that surrounded him is untravelled ground. Simon Sebag Montefiore, acclaimed biographer of Catherine the Great's lover, prime minister and general, Potemkin, has unearthed the vast underpinning that sustained Stalin. Not oinly ministers such as Molotov or secret service chiefs such as Beria, but men and women whose loyalty he trusted only until the next purge