The Defining Session

[Hal]

I've got an idea brewing for a campaign setup, and I was hoping to get some help from the playgrounders.

Here's the idea: While the players are still building their characters, have the first session using pregen characters. They're planning mercenaries, infiltrating a BBEG's lair to sabotage/steal his plot device. The session ends . . . somehow. Capture, death, party betrayal, something to that effect. The players don't get to walk in and walk out.

After the campaign has been going a little while, the characters get a new mission: "Hey, we sent out a team a while ago and they never reported back. Go check up on them."

I want this to be a thing where what the players did in the initial session defines what they'll encounter later on. The thing is, I'm having trouble coming up with situations that could vary enough for future outcomes to be both interesting and unexpected.

Any ideas on making this work?

[Sstoopidtallkid]

First, whatever method they use to sneak in is blocked afterwards. The ones they kill of course have been replaced, but their replacements are probably weaker. And don't forget, your players won't know what would have happened if they'd done something else. Cosmetic changes(the sleeping guard who they woke up and captured them has been re-assigned to a higher-priority post where he is...sleeping) will make the players feel like they had an effect even if they really didn't. Any captured PCs should be alive, but tortured/traitors.

[Reinboom]

I've had done something semi similar, but it was between session.
At the end of a session, after the players had captured a major NPC and had her locked up, I had asked if any of my players was willing to try a 1-shot with pregenerated characters so I could test a dungeon design I was working on (which is not abnormal for me).
What was actually occurring was a very strong what if situation, in case the party announced at any time that this person was captured. In which case, the grape vine of spies would instantly alert, and notify the rescue plan. In this case, a couple members of the party was the actual rescuers of that NPC.

I had them roleplay these characters, saying, this is a spell locked hold of a prison, underground. Via a situation of corrupted influence of the above guards, you managed to get down this far unnoticed by more noble officials. From here on, however, you have a connection to nobody, and everything in here, except your target, is an enemy.
The target, a tall elven woman with long straight and flowing black hair who goes by the name Kyra (the party didn't know her real name at the time, so, they didn't make the connection) is who you are trying to get out. Your lives are unimportant, because, you realize if you are successful, you will be rewarded and brought back to life if found dead. Just get the target out.

The party members did a very decent job at adhering to this. They didn't manage to get her out though, only just barely faultering.
However.. future party actions caused her to escape. The game was greatly influenced by what occurred in this situation, however, and I think my players enjoyed it.