OK, here's what I'm thinking of so far:
The basic problem is that when the players act realisticly, the plot will stop dead in it's tracks. So there is text telling how to force them onto the rails. Not my style.
Now the plot calls for *good* people to be doing a devil's handiwork. So my main idea right now, it that there are some fallback adventurers who are also good, and also caught up in the plot. They are NPCs that players like.
And, to be extra evil, they may comprise PCs that the players have retired to start new PCs. Not dead, not given up on, everyone likes "Old Stumpy," it's just that the player wanted to explore a different type of character.
I anticipate howls at this point. "Well, you said he was staying active."
The 'B' team.
1. In the Freeport setup, what if the players refuse the call to adventure? They know not to trust anyone in Freeport, but then again, in Metagaming, they may think "Oh, the hook. Pretty dumb, but what the hey!"
Instead of geasing them to do it anyway, plan B uses the geas trick, but on party B. And the players find out. Maybe being geased doesn't mean you can't send a call for help!
I'll add a second pirate ship, and the Hell Pirates will be hopping mad that it just got stolen.
2. The Freetown Setup. If the B team is already in action, no worries. The mayor's already sent them. The A team might want to go to help them, as it could be dangerous. This is hell after all...
If team B isn't in the game yet, and the players balk, "Oh well, hope that other, weaker, Team B, can do the job by themselves."
3. The capture the PCs scene. If the PCs are kicking butt, they will have to break out their friends from the prison. If Team B hasn't been neccessary yet, add a clue after the battle, or even during. "You fight almost as well as that Dwarf Stumpy, but it did him no good. Surrunder fools!"
Comments? Other paths that keep the adventure moving?