We played our second session of ICONS last night, and I was not a fully prepared GM. I had miscalculated. I was completely ready to finish the previous (published) adventure (The Skeletron Key), to simply show up and play Heroclix, or to play some combination of the two. But throughout the day before the game, I started to get the feeling that the players who showed up for this game wouldn't have a strong overlap with players from the first game. So, I downloaded the second (published) adventure for ICONS (Sins of the Past) and read/skimmed about 3/4 of it on the el on the way home from work.
Surely enough, we had four players, but only one from the original game. So, we played the new adventure. Like the first adventure, Sins of the Past was a real railroad. I'm generally not into railroading my players, but I understand that non-sandbox adventures tend to be railroads, and the GM just has to deal. When I've run railroady adventures in the past, I feel like I've done well on the fly modifying the adventure to fit what the players do. But this time was different: I simply didn't know the adventure well, and I hadn't read the ending before we started playing.
I think I did alright at the beginning. Within literally the first 10 minutes, the players had left the tracks. They were supposed to form a friendly relationship with the Golden Agents - a classic superhero group from the WWII era - and the Golden Agents would help lead them through the adventure. But the relationship didn't work out this way. This was partially because of my actions. In the earlier game, one of the characters threw a helicopter into a skyscraper, and the one repeat player wasn't very popular as a result. The Golden Agents reacted accordingly. For the most part, this worked out fine, and we managed to progress through set scenes in the adventure with a plot reconstructed on the fly.
But I made a bad decision at the end, right as we got into the part that I had quickly skimmed/not read at all. The characters by all rights should've captured a super villain (a talking monkey with a tommie gun!), and I didn't let them. My actions were a little believable, given the capacities the villains had shown in the past, but they were way too facile - a probability controlling teleporter snatched the hostage away in a single turn. In retrospect, I realize that I did this out of desperation - I simply didn't know what was coming next, and a hostage was the railroaded outcome of the scene (which in turn would lead the PCs to the next scene). Now that I've thought about it and read the full adventure, I know that I clearly didn't need to do this. So, I'm thinking about a retcon to even things out in the next game.
But I still feel like I made a rookie mistake: I railroaded the players with a bs move to further the pre-existing plot. I know that kind of thing can grind. Just goes to show that you shouldn't fly blind down the railroad tracks.