Not my current campaign, but a previous one - two players played as brothers in the game. They wanted to seek revenge for the senseless slaying of their younger sister. One brother was a wage slave at the company which was found to be behind the murder. So he quit and joined his brother who he hated for years for being a nobody hood-rat. So, they then needed to hire someone else to do some other work (Mage). So they met Mr. Johnson and were told to go meet the mage character. So, cut to, I start the Mage character out In Media Res - middle of a fight. The brothers save him and they join up. On the second scenario, another friend wanted to join the gaming so, we said that he was an old contact of the street-rat brother, ex-military type who needed some money. So, I had those four players for about 20+ scenarios. Always lingering in the background was the revenge plot, which I had worked into some of the published adventures by either adding a side quest, or dropping some info along the way or changing one of the baddies to one of my perennial baddies.
It was fun.
Still working on my new SR5 campaign meet-up scenario.