The makeover in superhero movies is usually more dramatic than in Undercover Boss (Channel 4, Tuesday 9pm).

No facepaint or titanium vest for Poundworld troubleshooter Martyn Birks, just a denim jacket his wife said, rather kindly, made him look “like Jack Nicholson”. Pants stayed beneath trousers at all times.

Poundworld turns over £150m a year (that’s 150 million items sold a year, maths fans). But staff retention is poor and training costs money: in particular, teaching staff the patience to explain dozens of times a day that, yes, everything in the shop is £1. Yes, including the biscuits. Yes, just £1. Sigh.

Looking less like a celebrity hairdresser than founder Chris Edwards, Birks blended in well. Embedded in the High Wycombe store as fictional societal dreg John Farmer, he bantered affably with everyman Dave, who branded the products “crap” to break the ice.

Store manager Ian (played by Lord of the Rings’ Sean Astin) was the first decoy villain, a graduate who “accidentally got promoted” instead of living the IT dream. Things didn’t go well. After deductions for not clocking in and a whopping discrepancy on his till, ‘Farmer’ had earned just £22 for two days’ work.

European ice queen Malvina (played by Scarlett Johansson, or maybe Christopher Walken in drag) ran the Nottingham store with an iron fist. Its sky-high returns were inverse to rock-bottom morale - and Birks was visibly shocked, while Malvina was revealed as a mewling kitten on the inside, dreading a spin in the Head Office tumble dryer.

In a Memento-style twist, Birks himself emerged as the villain. Peeling off his alter ego to reveal the suit underneath, he was masterfully creepy in his debrief with the underlings, like Anthony Hopkins in Oscar-baiting form. It made for uncomfortable viewing as Dave - who’d likened the HQ summons to “being on Death Row” - teetered on the brink of the sack.

But Birks couldn’t keep it up. Everyone got a free holiday, while Ian was promoted, perhaps in return for shedding his woeful beard. A £250,000 plan to jazz up the staff areas was also unveiled.

While life is rarely much fun on the shop floor, functioning air-con probably helps.