It's just that three Adventure Cards got played, and each one put a hard 112-degree turn into my prepared narrative.
My main plan was to tie them up in a complicated situation. I often throw "Kobayashi Maru" scenes at players, where there is no right course of action, and a high likelihood of misery and trouble no matter what they do. The idea being that you great roleplaying and memorably intense scenes, at the small cost of bogging down the plotline for several hours. In this case, the prepared scene could easily devolve into inter-party feuding (or even one PC arresting another), a very bloody 3-way battle with cowboys and a witch, curses on the whole group, death by evil tumbleweed, and a knife-fight with the peg-legged cook.
Yesterday, though, the PCs were able to sidestep everything easily, thanks partly to the Adventure Deck. Everybody drew real powerhouse cards. One got played that made peace break out. It took most of the wind out of my sails, diffusing the tension, and the players thought and acted quickly in its wake. Problem solved (about 2 hours early) without any bloodshed.
All of two minutes later they played a card that gave them an additional supernatural advantage in chasing after Cobb. I had easy ways to counter this, and would have felt justified, since no one card should short-circuit the plot. However, I really wanted to reward the PCs for handling things so well and being so determined. So I gave them a glimpse of Cobb high on a ridge before them, now only a few hours ride ahead of them (minutes if they left their horses behind and piled into Dr Immelman's flying machine). Cobb spots them, and starts testing the wind, like he expects his pistol to have the range of a modern sniper rifle (it is The Gun, afterall).
Down comes another Adventure card. This one causes a case of mistaken identity, to the players benefit. Cobb thinks they're someone else. So he shoots a bird, reanimates it, and sends it flying to the PCs. It lands in a tree, and it's beak twitches with Cobb's voice. "Which one of you is Hoyle?"
An aside: In Deadlands, the laws of magic were codified and "popularized" by Edmond Hoyle, author of the book of rules to card games. Officially, he's been dead 100 years, but then, Cobb's got several slugs lodged in his eye, so it's not impossible Hoyle might be up and about, too.The session ended with the PCs bluffing a bit to their intentions, and arranging to meet up with Cobb and "posse up" together.
For the record, I'd planned on having the chase for Cobb last about 8 sessions (and I tend to over-prep, so 8 could easily become 10 or 12), but between determination, cleverness, and good cards, it looks like the PCs will be in pistol range on session 4. (We'd been playing once a month, due to scheduling conflicts, but that's cleared up a bit, and the next session will be two weeks from yesterday.) I'm excited, as much fun as the chase has been - the confrontation should be far better.