‘Do you think one day we could get a massive TV like this one?’ says the oblivious Lily, Sam’s youngest, as she lies in a middle-class household and gazes at a plasma screen while her mum cleans it.

It’s a naively hopeful question, something Sam knows is virtually impossible to fulfil considering their current situation. But Sam’s own aspirations of wealth start growing to similarly naive proportions as she plunges deeper into the world of insider trading.

While she’s cleaning, Jess (Jade Anouka) finds another phone belonging to the suspended insider trader Blake (Ben Bailey Smith), which holds all his correspondence with another trader known as ‘Swanney’ (Lloyd Owen). Sam (Sheridan Smith) takes advantage and decides to meet face-to-face with Swanney, while pretending to be a silent partner of Blake’s.

Sam (Sheridan Smith) is determined to recover her losses

There was a fear that writer Mark Marlow would fall into a predictable formula, but thankfully he inserts some thick suspense into episode three. As well as being questioned by the firm about the microphone in the vent, Sam also takes on a special persona, ‘Nancy’, to gain Swanney’s confidence.

These are the episode’s strongest moments. Sam treads confidently towards this illegal, risk-driven world – her guise filled with wealth and knowledge, which she clearly wants for herself. She even steals from her middle-class clients to give legitimacy to ‘Nancy’. Picking up snippets of conversation from wandering stockbrokers around Canary Wharf, she adopts all the characteristics she needs for her own personal undercover operation.

While cleaning for a middle-class household, does Sam see what she wants?

The more domestic areas of Cleaning Up have become less interesting, unnecessarily expanding Sam’s character rather than moving the plot along. Lily’s (Anya McKenna-Bruce) issues with girls at school and Dave’s (Matthew McNulty) recently hospitalised mother serve only to fill time, with Marlow struggling to find enough relevant material to stretch over six episodes.

But things start to pick up towards the end as Sam gains another accomplice and goes to meet a gaggle of insider traders. An excellent, eye-pulling twist arrives in the episode’s closing minutes and promises to turn the whole series around. Hopefully, episode four will take the more engaging route: the one with all the money and all the plot.

Cleaning Up continues Wednesdays on ITV at 9pm