"I had no time to Hate /Because/ The Grave would hinder me / And Life was not so / Ample I/ Could finish  Enmity ". These startling lines were written by Emily Dickinson in 1862. While she thought better of taking the lid off hatred within her lifetime (the poem concludes that to pursue "The little Toil of Love" is a more apt ambition), those who helped forge her posthumous reputation, it seems, did not. Lyndall Gordon's new biography focuses largely on the incendiary feud that followed Dickinson's death, and which both distorted and helped build her reputation as one of the most fascinating poets who ever lived.

The book's first half summarises, in a racy, sometimes elliptical way, what we know of Dickinson's life. Gordon poses some fresh angles, most notably an entirely new theory about the nature of the "illness" that caused Dickinson to gradually withdraw from the world and was the cause of the profound psychic disturbance evident in many of her poems. Gordon's proposition, that she suffered from epilepsy, is persuasively argued, even if one is left feeling that only a small part of the real story has been told.

The second half grippingly recounts the torrid drama that unfolded after Dickinson's death, aged 55, in 1886. She left 40 homemade booklets, containing around 800 poems, and at least 1,000 more kept chaotically on loose sheets, the backs of envelopes, even a chocolate wrapper. These became the possession of her sister Lavinia, with whom she had lived all her life. Asked to burn the papers, Lavinia destroyed Emily's correspondence but could not bring herself to do away with the precious poetry. Instead she gave some of it to her sister-in-law Susan Gilbert Dickinson, the wife of her and Emily's brother Austin. When Susan's efforts to get the poems published proved unsuccessful, a disappointed Lavinia turned to Austin's much younger lover, Mabel Todd. Ambitious and brilliant, Mabel flourished as copyist and editor where Susan failed. The toxic rivalry between the two woman, as well as Mabel's subsequent falling out with Lavinia, are the dramas at the heart of this work.

Gordon re-examines the details of a fight that raged through two generations. (Both Susan and Mabel had daughters who dedicated much of their lives to defending their mothers' positions in the feud and continuing to defend what they believed to be the "right" version of "their Emily"). Gordon's reading of the research reveals Mabel to be highly manipulative, responsible for a dedicated slander campaign against Susan, and for trying to cut her out of the Dickinson history entirely.

To those who know and love the modern editions of the complete poems and letters, Susan's place is not in doubt. Yet it is true that previous biographies have tended to echo the line that Mabel "sold" Dickinson's first biographer, RB Sewell: that Susan was, if not lazy, alcoholic, violent and monstrous, then at least an unpleasant character whom Austin possibly never wanted to marry in the first place. In fact, as the poet's work and other correspondence testifies, the truth was quite different. It feels unfortunate that, in defending Susan as the wronged woman, Gordon creates another melodramatic villain in Mabel. The truth, one hopes, lay somewhere in between.

Rebecca Swift is director of The Literary Consultancy. Her Dickinson: Poetic Lives is published by Hesperus Press