How About a New Writing Prompt

Three friends meet up regularly on Saturday mornings in one of their backyards with their dogs for a 'puppy playdate.'  As the dogs run around and romp, the three friends stand and chat and catch up.  This week, a fourth person shows up, unexpected.  Why did they come?  Did they bring a dog?  There is some reason, issue, argument, secret, need, interest, desire that led them to show up.  Are the friends all women, men, mixed?  What's the gender of the new person?  Did any of the three know this person would be showing up?

This is really open ended for you.  Maybe one of the dogs bit this person.  Maybe this person is coming to ask out or propose to the host?  I'll stop giving you suggestions.  What happens?