What’s the relationship between the two speakers?

M: Hello, Winnie. It’s me--David. Do you remember--from the party?
W: Oh yes, of course. Hello, David.
M: Listen, Winnie, I was wondering if you were doing anything on Friday evening? Only, if not, would you like to come to the Stratford for the day? They say The Cats is really marvelous.
W: Yes, I’d love to, but wait a minute--I’ll just check in my diary. I’m awfully sorry, David, but my mother’s coming down from Edinburgh and I’ve promised to go shopping with her un Friday evening.
M: Oh, what a pity! But can’t you go shopping another day?
W: No, I’m afraid not. My mother’s only staying for a few days.
M: Bat do you really have to go with her? Can’t she go on her own?
W: Well, she’s buying a coat and wants me to go along and help her choose it. I’ll have to go with her. She’s been looking forward to it for weeks.
M: Ah well. Another time perhaps?
W: Yes, fine. Look, why not the weekend after next? It’s still on then.
M: Yes, I think so. A week on Friday, then. I’ll pick you up at about two o’clock. OK?
W: Yes, lovely. Thank you. I look forward to it.