Let's Kill Uncle drew me into a deliciously horrible adult world, published in the Guardian / by Rich Hobbs

I know it was in the year after my mother died when I was 10, though I can't remember whether it was my sister's Girls' Brigade troop fete or a church jumble sale we turned up to just by chance. Part of me, 44 years on, seems to remember being there with my friend Clive Brazier and his mum, though maybe I was there with my father, spending another typical weekend sniffing out a bargain. And though I couldn't now say whether it was in Pinner or Ruislip, in my mind's eye I can clearly see the secondhand book stall by the path leading to the church or community hall, the lawn around it dappled with sunlight, where I bought a tatty paperback edition of Rohan O'Grady's Let's Kill Uncle.

This jumble of vagueness and clarity over the details of my copy's provenance is strangely appropriate. The book itself is not well known, though over almost half a century I've reread it often enough to feel I know large parts of it by heart. In spite of its obscurity, three years after it was published in 1963 it was turned into a movie. I've never seen this film, and because most of the scenes in the book are photographically precise in my imagination, I never want to.

It wasn't until I was in my late 20s that I finally twigged that Rohan O'Grady, regardless of my clear perception until then of him as a short, wiry, black-haired Irishman, is in fact a woman called June Skinner, now 92 and still living in her native British Columbia. I've never read any of her other four novels, and naturally assumed Let's Kill Uncle had long been out of print until I was asked to write this article. Then I found out Bloomsbury reissued it in 2010 with a glowing encomium from Donna Tartt on the back cover. So it was very recently that I discovered the book was first published with a frontispiece by one of my cartooning heroes, the great Edward Gorey, laureate of the macabre.

And who knows what first sparked my interest in this book. My original Mayflower edition, from September 1966, now Sellotaped together and its pages yellowed and smelling, mysteriously, of chocolate, says on the cover that Let's Kill Uncle is "the most readable blend of humour, horror, chills and child psychology since High Wind in Jamaica".

I now know that the film of High Wind in Jamaica featured the young Martin Amis, but back in 1970 neither he, the book nor the film meant a thing to me. Did I think it was something to do with The Man from U.N.C.L.E., or even with JP Martin's Uncle series of books for children, about the heroic philanthropic elephant? If so, it's interesting that things that would have appealed to me as a child in fact lured me into a deliciously horrible adult world, both captivating me and capturing me at precisely the right moment.

Whatever it was, just at the time when I was achingly conscious that my mother's recent death had ushered me out of childhood and exiled me into something quite different, I became absorbed by June Skinner's gruesome little book about two children called Barnaby and Christie, around my age at the time, on holiday on an island off the coast of British Columbia, who conspire to murder Barnaby's uncle before he murders them.

Which is how this book changed my life. Some might say that it's hard to think of a book less suitable for a child of my age and circumstances, but without me even realising it, Let's Kill Uncle transported me into an enormously comforting realm of the imagination, that shadowland where we recreate and reorder reality to make it bearable.

So, I began to understand that horror can, and often should be, played for laughs; that death, in the right hands, is funny; that dark humour isn't "sick", but one of the best medicines there is. And as I kept rereading it at that formative age, the book was also ever so gently nudging me towards my ultimate career path.

And it's consistently more rewarding each time I reread it. A couple of weeks ago I suddenly recognised that Uncle Silvester – the eponymous object of the two children's murderous intentions – is clearly based on Sylvester the Cat from the Warner Brothers' cartoons, only darker and more, well, Goreyish (though the bit of business about the death – presented as murder – of Fletcher the Budgie is a big hint).

Likewise, I've only just clocked exactly the depth of the darkness of the shadows that the Holocaust casts over Sergeant Coulter the Mountie's reflections on innocence and wickedness. Then again, when I was 11 it would never have occurred to me that the book was written shortly after the Eichmann trial, and Hannah Arendt's famous observations about the banality of evil. And I've not even mentioned One-Ear, the self-pitying, soliloquising cougar who ultimately fulfils the role of deus ex machina in the book.

I could go on forever with a line-by-line exegesis of Let's Kill Uncle. I could even try to articulate why the ending – with its interplay of innocence, guile, triumph and cynicism – is so desperately moving and yet also ghoulishly funny. But then again I don't want to ruin the plot for you. And I do want you to read it, with an almost evangelical fervour.

It's not the greatest book ever written, nor will it detain you for long. But it should make you laugh, and make you think, and possibly even make you cry if you have a heart at all. I can conceive of no greater recommendation than that.