I GM a Shadowrun group for a campaign that is the baby of one of the current players. He and I GM together, but right now I run all the sessions and he's playing and doing some of the planning with me. He also has stories that run in the background, so to speak, that I don't know about, which is usually fine with me. But the other day I got blindsided by one.
We were doing a Play by Skype with another player, between Fog and Kiki, who are in a relationship that is a bit rocky to say the least. Fog is a full PC, Kiki is an NPC/sometimes PC. They fought and Fog took off for some time to think. Kiki went back home and then just disappeared. Nowhere to be found.
And I was like: WHAT? I had no idea this was coming and my brain went into overdrive, trying to calculate how this would impact the stories I had planned. Since Fog is a fairly central character to the group and his freaking girlfriend had just dropped off the face of the earth, the impact would potentially be huge. I asked, as the GM, what had happened to Kiki in a private chat and got a glib 'I don't know' as an answer, which I know to read as: 'I know, but I'm not telling you'. And I lost it, I was so incredibly pissed.
I mean, I'm totally okay with not knowing the reasons behind this. But I am NOT okay with having such a bomb dropped on me out of the blue when I do a lot of work of planning how the campaign is going to go in the long run as a GM. This had the potential to mess up my plans big time and it came from my co-GM. I seriously don't know why he didn't just tell me before. We usually do that for stuff we have planned, even if it's just: 'yo, this thing might happen, just a heads up'. In the end, we talked it out and we're good. The way this plays out is that the group won't be able to find Kiki anyway and I can just handwave her disappearance and the search for now. It will come up again, of course, but it's not derailing everything.
The reason why I was so angry was not that this might have overthrown all my planning. That's basically in the job description for any GM: plans won't survive contact with players. I like this about GMing. But if you have a co-GM, do not drop something like this on their head without warning. It's not necessary and disrespectful of the work they do. Much better to share and come up with a way to fit the story into the campaign together.