Letters of Ted Hughes, Selected and edited by Christopher Reid

This is a thoroughly exciting and absorbing book, as gripping as a good novel but tragic as only a true story can be. It's a tale rich in dramatic irony; its protagonist is complex and fascinating, laden with contradictions he was seemingly unaware of. Despite what one must assume were the best efforts of Hughes's devoted publishers, he comes across as fairly bonkers.

Christopher Reid was, as he explains in his introduction, Ted Hughes's editor at Faber for the last eight years of Hughes's life (he died in October 1998). His fondness for the poet is palpable, yet there are a few sly jokes between the lines. We sense the dry relish in the editor's footnote, after yet another of Hughes's attempts to have his books published on astrologically auspicious days ("please try and fix it. May 9th is a Tuesday"): "Wodwo was in fact published on 18 May 1967."

Many of the letters outline Hughes's own poetic practice, and will send readers back to the verse – his thoughts on Gaudete and Birthday Letters are particularly interesting. But the dynamite is in his writings to and about Sylvia Plath and Assia Wevill, the wife and the lover who committed suicide eight years apart, the latter taking their child with her. There are rapturous love letters to Plath, and few warning signs as their tempestuous marriage progressed. The crash comes as a psychic shock to all concerned.

In Autumn 1961, he is writing ruefully to the soon-to-be-married poet Daniel Weissbort: "Marriage is a nest of small scorpions, but it kills the big dragons." Within a year, addressing a newlywed, this has ominously reversed: "Marriage... is a bloody monster, but it eats up many little snakes." Hindsight renders his last few letters before Plath's death horrible, in particular his comment to his sister in late 1962: "You're right, she'll have to grow up – it won't do her any harm."

After Plath's suicide in the early hours of 11 February 1963, his pain and guilt are palpable, though a self-exculpating theory forms fairly quickly. There's an exquisitely bullying letter to Plath's mother, culminating in what looks very much like a threat to make contact with Plath's two children difficult. His justification is her overanxiousness: "We cannot protect their lives too much from life," he says. This contrasts oddly with Hughes's later attempts to limit or censor publication of material about Plath, claiming her children would be damaged by the knowledge. When A Alvarez publishes The Savage God, with its conjectural memoir of Plath's suicide, Hughes's response is barely sane: "You... didn't realise you were sticking electrodes into her children's brains."

Eerily, what he writes about Wevill's suicide echoes earlier comments about Plath's. "I look on her [Plath] as my wife and the only one I shall ever marry"; "Assia was my true wife." But within six months of Wevill's death, he was living with Brenda Hedden; and the following year he married Carol Orchard.

There are compressions and strange elisions here, and the absence of letters to Carol Hughes makes her the second Mrs de Winter to Plath's Rebecca. There's no hint, either, of his subsequent affairs. Still, the book can't be said to be a whitewash. As a portrait of a flawed man who struggled titanically with his own psyche, it succeeds brilliantly.