The new Channel 5 (I know! Me too – but yes, it’s still around) thriller Number One Fan stars two Coronation Street graduates from back in the days when the soap was still good. My peak Corrie-watching years were early 90s to early 00s. Which means I was there when it looked like the crowns were about to pass from queens such as Rita, Vera and Bet Lynch to their honourable successors, like Shelley Unwin, Karen McDonald, Fiz – and maybe to a younger Battersby or two, if the family learned to stop yelling and give us a bit more northern wit. Alas, their reign was brief and now there is no question that Coronation Street is worse than it has ever been. We do not have time to get into this now. Suffice to say: the presence of Sally Lindsay (Shelley, as was) and Jill Halfpenny (Rebecca Hopkins, of the same era, as love interest for Martin Platt) is enough to assure you of a good time.

Here, Halfpenny plays Lucy Logan, a beloved daytime TV presenter with her own, mildly emetic show, a sponsorship deal for her onscreen wardrobe, and a new line of pampering products coming out under her name, in partnership with a brand-friendly charity. Apart from the monthly box of expensive truffles that are actually made of manure (I want to know who bit into the first one and discovered this; a bad work experience week for someone, I reckon) sent by an unknown non-admirer, life is good.

Even when she has her bag snatched in the supermarket car park there is someone on hand to rescue her – Donna (Lindsay), ex-military and a big fan of the show. She gladly accepts an invitation to the filming and a tour of the studio (“This is the best day of my life!”), but declines the opportunity to be interviewed. As Lucy sends her away loaded with skincare products, a designer jacket and gratitude, she tells her not to be a stranger and come by any time. That turns out to be a mistake.

There Donna is, front and loudly centre of every taping for weeks after and possibly also outside Lucy’s daughter’s school, though Lucy thinks she may have been mistaken. It’s less hard to misinterpret the multiple bouquets of flowers and the message written in lipstick on her bedroom mirror – “You inspire me xxx” – left in Lucy’s house while she is out.

From there, things escalate and start twisting. This is not a wildly sophisticated drama – it lives or dies by its plot and the fun you have on the rollercoaster – so I want to stay as clear of spoilers as I can. If you have watched four-part weeknight thrillers before, I’m going to guess it won’t ruin the suspense too much if I say that Donna’s presence in the car park before the mugging was not by chance (“Drop the act, I know it’s you, you creepy cow”), and that she has a deeper, darker motivation behind her stalkery business than acquiring freebie jackets and exfoliating scrubs, and wants revenge for greater sins.

If I were a betting woman, I’d place quite a large sum on the truffle-sender – of whom we get occasional glimpses, generally involving him shouting at the Lucy Live show or throwing darts at a picture of Lucy’s face – being involved with it, too.

Add to the mix a husband in financial trouble, a son drawn online into an eco-activist group that is moving towards violence, and a daughter who is the right age for getting into a car that looks just like the one driven by Mummy’s chauffeur, and four hours of harmless fun is pretty much guaranteed. Its success depends hugely on having two leads who can sell anything and are constitutionally incapable of hitting a false note, however preposterous the happenings around them. Halfpenny or Lindsay or both are in just about every scene and they get the job done. If they could find their way back to Coronation Street some time and sort that out too, what a wonderful world it could be.