Motorway services waitress Margaret Mottershead and her colleagues head to London to join the audience for TV show Magic Moments. Meanwhile, at Heathrow, Patricia Bedford, star of American soap Glamor, arrives to a media circus.

While Margaret enjoys the show, an irritable Pat is backstage. The spotlight moves through the audience, falling on Margaret. Presenter Maeve explains that Margaret's sister, Pat, left after a row with their mother when Margaret was 10 years old; the two have never met since. Margaret's lost sister, she reveals, is none other than TV star Patricia Bedford. Pat is as stunned as Margaret, but recovers her poise to stride on, and the two women embrace.

Afterwards, Margaret wanders the empty studio, bewildered, and runs into Pat, who is entirely uninterested in her, coldly suggesting she get on the coach back to Lancashire. Crestfallen, Margaret heads off, but Pat's pregnant assistant, Claire, convinces her to come to the after-show party. Rushing to fetch her friends, Margaret watches their coach drive away.

Pat despatches Claire to send Margaret away, but Claire takes pity on her. A reluctant Pat is forced to accommodate Margaret in the Regent Hotel. The next day, horrified that the revelations about her humble roots will destroy her career, Pat offers Margaret money to keep quiet. But when a TV crew arrives, she resigns herself to a week of staged bonding for the cameras. Margaret phones her boyfriend, lavatory attendant Jim, but his disapproving mother withholds her message.

The newspapers invent quotes in which Margaret dismisses her old job and friends and looks forward to life in LA. Overhearing Pat badmouthing her on the phone, Margaret determines to leave. But when Pat spots a newspaper reference to their hated, ex-prostitute mother, Vera, she panics, begging Margaret to accompany her to Lancashire to stop Vera from talking to the press. Margaret reluctantly agrees.

With dirt-digging journalist Stella Kincaid is already heading for Lancashire to find Vera and ruin Pat, the sisters depart, with Claire instructed to meet them that evening in the Kirkby Arms hotel with Pat's bags. Meanwhile Jim arrives in London, where he meets Claire. The two drive up North together, until Claire realises she's forgotten Pat's bags. They wait with Jim's domineering mother while the bags are driven up from London.

Pat and Margaret find a Vera in a retirement home, but she is not their mother. At a garage, they spy Stella and photographer Billy. Hiding, Pat is accidentally sprayed with water from a jet wash. Margaret buys her a cheap shellsuit. They find their old home boarded up; for Pat, the memories begin to flood back.

Turned away by the Kirkby Arms because Pat has no money or ID, and by Bella because of the newspapers' stories, the sisters go to Margaret's dingy flat. Jim arrives with Pat's bag, but won't stop because he's worried about his mother. Margaret, irritated, breaks up with him. Claire and the disconsolate Jim are spotted by Stella, who gives Jim a note for Pat, saying it's from 'a fan'.

The sisters talk. Pat reveals that she was thrown out by Vera because she fell pregnant; Margaret tells her she too was abandoned after Vera was imprisoned for prostitution. Pat takes Margaret to an old haunt, the Swiss Cottage Café. The owner, Pete, reveals he's planning to sell up and retire. Claire joins them, and gives Pat the note.

Following Stella's anonymous tip-off, Pat and Margaret find Vera at her luxurious house, bought with Pools winnings - now gone. Vera greets them coolly, and is unrepentant. Outside, they find Stella and Billy. While bailiffs remove Vera's possessions, Stella makes a surprise proposal - a sympathetic story of Pat's tragic past, in return for exclusive accounts from her and Margaret. Vera, of course, will have to be tied in.

Margaret and Jim patch things up when he finally agrees to leave his mother and live with her. At the airport, the sisters embrace and Margaret promises to visit. Pat hands Margaret some keys and a letter. Pat waits for her plane with her travelling companion... Vera.

Some time later, Margaret and Jim happily clean up at the end of a shift at the Swiss Cottage Café.