Terminate the call.

You get a sudden feeling of concern. You're not sure if it's a sense of betrayal to Sandra, that this is some strange stick joke, or simply a desire not to deal with a professional sex-worker, but you text back: “Sorry not interested.” And hang up.

Wanting to put the whole thing behind you, you decide not even to call David and simply go to bed.

It takes a while to go to sleep as your thoughts soon drift back to thinking about Sandra.