The Poison Tree, ITV1

When watching an adaptation there are times when it's better to have no acquaintance with the original. That certainly goes for thrillers, in which the reveal is all, so it is with considerable smugness that one brandishes one’s ignorance of The Poison Tree. Wiki advises that it is a bestselling psychological thriller which has floated the boat of the likes of Richard and Judy and their estimable book club.

ITV’s two-part dramatisation tells of Karen, an introverted young mother whose husband Rex returns from a dozen years in the slammer. When Karen and their sprightly daughter collect him on the day of his release, a burly man in a beard is also completing his stretch. Not that you’d notice until the owner of the same mug turns up towards the end of ep one, threatening blackmail most foul, having previously worked his way under our heroine’s skin with various cold calls and envelopes full of long-lens happy-family photos.

This is a television thriller as mail-order catalogue, all pastels and decking

Who on earth, you may reasonably wonder, would want to blackmail anyone quite as bland as Karen (MyAnna Buring, acting without a scrap of make-up)? It turns out that she and Rex (Matthew Goode) made their acquaintance years earlier while at college via Rex’s flamboyant but highly doolally sister Biba (Ophelia Lovibond). Pill-popping Biba is by contrast trowelled in eyeliner and, we soon learn, damaged beyond repair by the suicide of her mother and the callousness of her yobby self-made father. It was his infidelities which started the trauma, and he has since begun a new family and even now is threatening to evict his older children from their home. Not any more he's not, because he's dead.

“The only interesting thing about you,” Biba advises Karen, “is me.” Well, not by the end of this episode it wasn’t, which culminated with the nasty father falling over the banisters and Karen shooting Biba’s dealer in the chest. We will find out exactly what prompted this outburst of charisma in episode two. If, that is, we are still watching.

So it seems Rex spent all that time at Her Majesty's pleasure to spare Karen from prosecution. People do things in thrillers they may not get up to in real life, but we happily buy into preposterousness if the stakes are sufficiently high, the characters compelling enough, the sense of danger ratcheted up to the max. That's a big if. This is a television thriller as mail-order catalogue, all pastels and decking. The atmosphere of hedonism and sinful hints of incestuous longing are soft-pedalled. Even the famously weird Dungeness, the shingly Kentish village where Karen is living the quiet life, has had the strangeness siphoned off. Buring and Goode are capable actors, but director Marek Losey seems to have instructed them to downplay the emotional stuff in order all the more to set Biba’s madness in relief. A logical notion, but it means an hour in the company of two characters who are dull even in extremis.

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