WORDSWORTH DESCRIBED CHARLES Lamb and his older sister Mary as 'a double tree / with two collateral stems sprung from one root'. They were the most intimate of companions, apparently inseparable. 'As, amongst certain classes of birds, if you have one you are sure of the other, so, with respect to the Lambs; observed De Quincey; 'seeing or hearing the brother, you knew that the sister could not be far off.' All who came across them remarked admiringly on their mutual devotion, and the abiding love thev showed for each other. Their shared interests - in books and in the theatre, for example - were enriched by common experience. 'If we may use the expression, their Union of affection is what we conceive of marriage in Heaven,' remarked another of their hiends, in a letter to his wife: 'They are the World one to the other.' Neither sibling was to marry. 'We house together, old bachelor and maid, in a sort of double singleness,' the mature Charles reflected. The Lambs cohabited almost all of Charles's adult life, and when Mary died, twelve years after her beloved brother, she was buried in the same grave. In death, as in life, they were together.

Yet this apparently perfect pairing was clouded by a dark secret, known to only a few. In mid-September 1796, at the age of thirty-two, Mary Lamb had begun to show signs, not for the first time, of mental instability. She was then worhng as a mantua-maker (a dressmaker), and living