From the introduction:
You have received an invitation from a friend named Anna to attend a makeover party, to try out a line of cosmetics she's selling as a side gig. You have reason to believe that you will meet contacts at the party to whom you must pass on the vital secrets you have learned from your spy work, and from whom you may learn more details to flesh out your partial intel. But when you arrive, you don't recognize any of the others – at least in their current disguises. For all you know, there are some normal civilians (or worse yet – double-agents betraying your homeland to the USA!) at this party. You'll need to disguise your exchange of intel in the form of trivial gossip until you're sure who you can trust.
...
Your secret briefing contains a code for painting other party-goers' nails. When certain events occur, you should paint one nail of the appropriate person the indicated color.