To start the series, Mary visits the wealthy town of Ascot. Its High Street is home to Blinkz, a shop that caters for the fuller-figured woman, owned by size 10 gym fanatic Amanda Collins. Mary is shocked to discover that Amanda's attitude to her plus-size customers leaves a lot to be desired. Blinkz is full of dowdy, baggy, unflattering clothes that most people, whatever their size, wouldn't be seen dead in. As a result nothing is selling and the business is in crisis.

Cardiff presents Mary with her most difficult challenge to date. Kelvin Evans, owner of a boutique and bar called Floyds, has very firm ideas about the retail business. Run by his partner Sharon Hunt, Floyds sells cheap end-of-line clothes and tacky accessories. The women of Cardiff are giving Floyds a wide berth, but Kelvin cannot understand why. Not one to mince her words, Mary lays it on the line and tempers flare.

Burt's Men's Store in Chorlton has been in Adrian Burt's family for 112 years but under his leadership the store's takings are worse than they've ever been. Mary Portas is determined that this store deserves a place on our high street but it's going to be a massive upheaval for the staff - one of whom has been working there for 33 years. She's got to bring the outdated Burt's team up to speed on 20 years of men's fashion.

Three years ago professional stylist Becky Eleazu realised her dream and opened Rumplestiltskin, a hip fashion boutique in an up and coming part of South London but when her boutique failed to attract the stylish locals she asked her partner Max, a personal trainer with no fashion experience, for help. Max has the gift of the gab but when it comes to fashion he's way out of his depth. The shop looks like a youth club and the clothes are way to "street" for the young professionals Becky wants to attract. Right now those shoppers are getting their fashion fix in London's West End and to get them to shop local is going to take a miracle - or some magic - from Mary.

Lucy Weller, a former theatre set designer, owns and runs Selkie, a ladies' fashion boutique in the centre of York. A fabulous building and a wonderful location haven't been enough to attract York's sophisticated forty-somethings over the threshold.

This week Mary visits two shops she helped put on the right track in the last series. Ju-Ju, a Brighton based fashion boutique, owned by Tim Price and Soly Daneshmand, had completely lost its way and was haemorrhaging money. and Doncaster-based shop Homeboy, which she'd renamed Seen as part of her strategy when she first visited last year. The shop had been struggling in the face of stiff competition from a new shopping centre that had opened in the town. But owner Cath Taylor had also lost sight of her customer and was not offering what the 'disciples of Beckham' tribe were after.