The Walking Dead is at its devastating best when it’s barely watchable.

From the outset, when Patricia cuts the legs off some live chickens out in the henhouse (their cries of agony are as disturbing a sound as this series, with its expert grasp of the aural, has produced yet) and then takes them out into the barn for the captive gaggle of walkers in the barn to get stuck into, Secrets is a contender for being the most unsettling episode of the series so far – and the most compelling.

It’s also the part of the tale – as the title indicates – where a lot of the things that characters have been hiding start to seep out.

The business of secrets, as Glenn has come to learn, is a pretty miserable one. ‘I suck at lying,’ he confesses to Maggie when she begs him to keep schtum about her father’s zombie stash, and soon he’s spilling his guts – not just about the gruesome guests out in the barn but about Lori’s pregnancy, too.

However, the First Lady of the group is as grimly determined not to let Rick know that she’s up the duff as her husband is to maintain discretion about the fact that Hershel wants the survivors to up sticks from his farm – and while there are no pills in the drugstore which can solve Rick’s dilemma, for Lori, it’s a very different matter. ‘This baby won’t have any good memories at all,’ she says whilst trying to make a dismal choice about the unborn child’s future, ‘only fear and pain.’

Speaking of scary things, Shane – the adventurous post-apocalyptic woman’s functional psychotic – allows his mask to slip whilst treating Andrea to an advanced firearms course. After bellowing in her face about killing and her dead sister for a few minutes, she storms off.

‘You’re a real dick, sometimes,’ she informs him when he catches her up. ‘I acknowledge that,’ he replies, and their mutual attraction – hinted at earlier in the series and given potency by the smell of gunpowder, the shouting, and the dreadful lack of internet pornography – boils over into unstoppable lust.

For once, we’re spared the gory details, but there’s none of the innocent charm of Glenn and Maggie’s liaison here. The thought of Shane on the job is like trying to picture a scorpion’s seduction techniques.

Most disconcerting of all, of course, is the insidiously good way the show lulls the viewer into a sense of dreadful normality. One moment, we’re gazing over a verdant meadow, crickets chirping in the sunlit tranquillity; the next, there’s an Uncle Fester lookalike with his head on at a jaunty angle making a beeline for the nearest bit of living flesh.

The lightning-fast jumps from calm to calamitous are enough to either give you a heart attack or send you diving behind the sofa for shelter – but not so far that you can’t see the screen. The more unnerving The Walking Dead gets, the more difficult it is to tear your eyes from it.

Airs at 9/8c on Sunday 20th November 2011 on AMC in the US.

Airs at 10pm on Friday 25th November 2011 on FX in the UK.

> Buy the Season 1 DVD on Amazon.

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