Memoir: On May 10th, 2002, the novelist Nina Bawden and her husband, Austen Kark, boarded the 12.45 train at King's Cross station in London.
They were going to an 80th birthday party in Cambridge, where there was to be "a boat on the river, a cheerful evening of food and drink and old friends making merry".
Fifteen minutes later, however, Austen Kark was dead: one of seven people killed instantly when, as the train approached Potter's Bar station at almost 100 mph, the malfunction of a set of points caused a disastrous derailment.
Where does it lie, this tiny, invisible line between life and death? Between normality - passengers on a train settling down with books and papers and overnight bags - and utter ruin?
In this short book, written in the form of a letter to her dead husband, Bawden deliberately runs her finger along it; she attempts to trace the untraceable, in the process posing a number of pertinent questions about grief, guilt, blame and celebration in contemporary western culture.
At one level, Dear Austen is a gentle, humorous tribute to the husband Bawden obviously adored, well stocked with memories of their life together and details of their plans for the rest of that summer, which included - ironically enough - trips to the Arctic and to New Zealand. The 80-year-old, Booker-shortlisted Bawden, however, clearly has no interest in writing a sentimental memoir.
"I dislike the word 'victim'," she declares. "I dislike being told that I 'lost' my husband - as if I had idly abandoned you by the side of the railway track like an unwanted pair of old shoes . . . You were killed. I didn't lose you. And I am not a victim. I am an angry survivor."
Badly injured in the crash herself, Bawden gradually begins to understand the legal issues which lie beneath the railway company's refusal to accept liability for the tragedy, or even to apologise to the survivors and the bereaved. The development of this understanding - "we had not yet realised that a child or an unemployed old person is worth nothing in law, since neither young nor old support anyone else, nor contribute to the economy" - and the deepening of the resulting anger, fuels much of the narrative momentum of Dear Austen.
Bawden is not afraid to lash out at those who "run" the UK's railway system - "Snakeheads" - or at the Labour Government which has, treacherously in her opinion, presided over its dismemberment.
She draws a number of caustic international comparisons, both positive and negative. The Swiss official who simply can't imagine a train being late: the Australian rail crash, on a similar scale to that at Potter's Bar, which prompted the setting up of an immediate public inquiry.
There has been no public inquiry into the Potter's Bar crash and, with the third anniversary approaching next month, the chances of such an inquiry being instigated by Tony Blair's beleaguered government must, frankly, be approaching zero.
Small wonder that, as Bawden confesses, she does not know how to end this letter to her dead husband. This should represent a major flaw in the book but is, instead, entirely fitting. In fact, there is not, in 130 pages, a wasted word or a smarmy sentence in Dear Austen. The balance between the political and the personal is beautifully sustained: the overall effect has the cogent punch of poetry, or a good song.
It will, no doubt, give rise to a host of facile imitations - a sort of "Dear Dead Person" deluge.
But that's originality for you.
Arminta Wallace is an Irish Times journalist