The meeting doesn’t really happen, a man is there along with Soup and the other man is show by Tom, a friend of the McMillans. This is the first of several members of the upper crust of San Francisco that are introduced in this episode. The two things all of them have in common is that they are in financial difficulties and they are going to a costume party that Mac doesn’t not want to attend.
One of the people going to the party has a necklace worth a quarter of a million dollars and she is determined to wear it to the party. Soup was trying to warn Mac about a jewel robbery and this woman’s house was hit the same night, but the necklace was not stolen. Mac has it appraised to make sure it wasn’t switched with a fake, but it’s the real deal and the police chief is convinced they will try again.
So Mac ends up going to the party to be part of the security detail. Just a bit of logic here, Mac is not a cop and has no police experience, although to be fair he did used to be in military intelligence. His costume is very awkward to run in so it was a poor choice and why is the police chief giving him orders anyway? Doesn’t Mac outrank him?