A mysterious figure gathers the players and hires them to do a job. Present since time immemorial, but formalized in Shadowrun, where corporations have anonymous people by the assumed name of Johnson give teams their jobs, negotiate payout, and deflect unwanted questions about who they're really working for. There have always been rich people who need deniable assets to do their dirty work, and the middlemen who intercede on their behalf - no questions asked, no questions answered. The players always have too little information, too good of a reward to pass up, and there's always a 50% chance that the Johnson is actually leading them into a trap.
A table of variations on thereof follow.
1. The Johnson meet, in which a mysterious figure (the Johnson) gathers the players and hires them to do a job.
2. The converse Johnson meet, where the players have gathered to give the Johnson a job.
3. The inverse Johnson meet, where the the players are the job: the Johnson shows up to meet the players, but they're just trying to distract the players until their hired guns can jump them.
4. The contrapositive Johnson meet, where the players are off doing a job that benefits the Johnson, but the Johnson hasn't hired them to do it. Johnson may contact them afterwards, as their interests are momentarily aligned.
5. The inverse converse Johnson meet, where both the players and the Johnson show up at the meeting intending to offer the other a job.
6. The converse inverse Johnson meet, where the players gather to kill a Johnson at a meeting under the pretense that the party is there to receive a job from them.
7. The converse contrapositive Johnson meet, where the Johnson shows up in the middle of the party doing a job, and offers payment for the party to stop doing it.
8. The inverse contrapositive Johnson meet, where the party shows up to meet with the Johnson, but after being offered the job the party then reveals that they did it an hour before the meeting and would like to be paid for it please.
9. The contrapositive converse Johnson meet, where the players have gathered to tell the Johnson that they've figured out that they're being sent into a trap and the job is off.
10. The contrapositive inverse Johnson meet, where the players and the Johnson get into a shootout as paranoid tensions that each is trying to betray the other boil over.
11. The contrapositive converse inverse Johnson meet, where the players gather to kill the Johnson at a meeting, but the Johnson offers the players a new job that's lucrative enough for the players to hold off on killing them.
12. The converse inverse contrapositive Johnson meet, where the Johnson shows up while they party's on a job, and tells the party they're very impressed with their work and would like to pay them for this job at a future meeting, presuming that it goes well... and perhaps if they accomplish a few side objectives along the way.
13. The contrapositive inverse converse Johnson meet, where several different Johnsons have all scheduled simultaneous meetings with the players in the same room, to each give the players a different, mutually exclusive job. None of the Johnsons know about the others, and assume the others are part of the party as well.
14. The converse contrapositive inverse Johnson meet, where the players and the Johnson realize they're both being played and team up to take on an even bigger threat that tried to manipulate them both into killing each other.
15. The inverse contrapositive converse Johnson meet, where the Johnson tells the players everything about the job, including that the party is going to be betrayed, in the hopes that the party uses this information to accomplish the Johnson's aims instead of the Johnson's employer's goals.
16. The inverse converse contrapositive Johnson meet, where the party runs into the Johnson in the middle of a job, and pays Johnson to finish the job in their stead while the party heads out to collect the reward they were initially promised.