Well, how comfortable are you with 4e? If you're new to the system, you may want to avoid anything fancy, but if you're willing to give it a shot, you could try an X-Files style opening, where horrific things happen to folks who aren't the main characters, in order to establish how dangerous the villains are.
So maybe run 3 encounters. In each, you have 1 or 2 players portraying their own characters, and everyone else is a 'pseudo minion.' Their purpose in life is to die horribly. Each pseudo minion becomes bloodied after one hit, and dies after two hits, or dies in one hit if it does more than 10 damage.
Pseudo Minion Stats
HP 10 (or 2 hits)
AC 14, Fort 12, Ref 12, Will 12.
Atk varies.
To make them fun to play, each pseudo-minion has one at-will, encounter, and daily power, chosen from the 1st level powers of a given class. I suggest picking classes the PCs won't be playing, just so they can have a bit of fun variety. The attack bonus with these powers is +5 with weapon powers, +3 with implement powers.
Explain to the players that, since this is a prologue, the main PCs will not die from damage. You're going to railroad them just a tad, but the goal is to immerse them in how they end up working together.
Act One
The barbarian sea captain and the fighter are on the same ship (maybe the fighter is crew, or a passenger), and the other players are random crewmen. The date is a few months before the first adventure, and they're sailing along the Shahalesti coast, heading for Seaquen as part of a normal merchant run (or pirate run, or whatever matches the barbarian's bacstory). Explain that normally they're allowed to travel this way without incident.
Extra Cast
- Sea Mage. Has thunderwave (for wind!), and other wizard powers.
- Boatswain. Keeps the crew in line. Has warlord powers.
- The Spy. Posing as a normal crewman. He's a half-orc being sent to Seaquen to link up with 'Damius,' who will give him further orders. Has rogue powers (including sneak attack).
They spot a well-armed, magically swift Shahalesti ship approaching them. The wind around the captain picks up, and a voice speaks to him, demanding they stop and submit to boarding, because divinations have revealed a Ragesian spy on board their ship.
It's up to the PCs to figure out whether to surrender, fight back, or negotiate (which will set the tone for interactions with Shahalesti later on). If they surrender, the elves board, grab the spy, then order everyone else to drop their weapons and chain themselves in the hold. If the PCs fight, well, the elves should be overwhelmingly strong enough to take them down, and the two actual PCs (non pseudo-minions), are taken captive.
The Shahalesti would consist of an eladrin mage and probably a whole lot of elvish archers (just reskin them as eladrin).
If the PCs negotiate, give them a chance to pull off a Diplomacy/Insight/History skill challenge. Success still doesn't let them keep the ship; the elves seize it either way. But the captain agrees to pay reparations. Whatever happens, the PCs end up in Calanis as prisoners or at least in custody for suspicion of spying. After a month they receive a letter that a friend in Gate Pass has paid to have them released. (Pick an NPC of your choice from Scouring to be this benefactor.)
The Shahalesti escort the PCs to Gate Pass and drop them off. If the PCs negotiated and succeeded, they are given a treasure parcel (maybe a +1 weapon, made by the Shahalesi) as reparations. If any of the pseudo-minions survive, they can become additional NPCs in Gate Pass, but won't actually join the party. The adventure ends a week or so before the campaign starts.
Act Two
This will vary a bit based on what part of 'the change in climate' you're talking about. Do you mean the cold, or the fact that (as revealed in adventure 6) there's a giant frikkin' firestorm hovering over the center of Sindaire? Also, depends on if the druid is in a tribe, or if he's a lone wanderer in the wilderness, or if he lives in a city and just happens to be a druid. I will assume he's part of a tribe; change as necessary.
The druid and a hunter buddy are out on the plains when they see a bloom of red light in the distance, like a giant flame. The sky rumbles with thunder, and they notice the clouds slowly turning red, starting in the distance and spreading toward them. It's a good bet that waiting around outside is a bad idea, but there's a town less than a mile away where they could take shelter.
When they get to the town, the town's priest spots them and yells for them to come into the stone church (a chapel of the Aquiline Cross), where everyone is hiding. Red rain has started to fall, and their skin burns wherever it strikes. Puddles of flame are already forming on the ground.
Extra Cast
- The hunter. An archer ranger.
- The apprentice priest. An invoker. (The head priest is an NPC with no magical power, but this is his student.)
- The farmer. A bard. He's just trying to protect his family from the strange storm.
- The knight. A paladin of the Aquiline Cross. He's trying to escort a minor Sindairese noble to safety, away from the Ragesians.
The noble in question spoke out against Ragesia's occupation of Sindaire, and when he heard that a rebellion was forming, he tried to reach Castle Korstull, which lies only a few miles to the west of this village. He was almost there when the army of Emperor Coaltongue arrived in a pillar of flame. A few roaming scouts of the army found him and his knight bodyguard, and he was wounded. He has been recovering here for several days. His hope was to reach Gate Pass, where he has friends (Councilman Menash, perhaps).
Feel free to have the noble and the priest answer any questions the players have (within reason), and when things are winding down, or when they ask a question you don't want to answer, they hear the firestorm abate. The burning rain has passed. The priest opens the church doors to see if the town has survived, and the moment the door cracks open, a charred skeletal hand reaches through and crushes the old man's throat.
Outside, a band of Ragesian soldiers who were slain by the firestorm and animated as sizzling undead try to enter the church. Use maybe four normal skeletons (with fire as just flavor), and one blazing skeleton that actually hurls flames. While two dozen non-combatants cower in the back of the church in horror, the PCs have a chance to save them.
A round into the battle, the old priest, dying but not quite dead, points toward the rostrum of the church, where a font of holy water stands. The priest gasps out his final breath, and suddenly the font begins to glow. If any character reaches the font and places his hands in the water, he begins to shed radiance, dealing 5 damage to all the undead each round, while simultaneously healing 5 damage.
If the PCs manage to kill the undead, great. That means the townsfolk survive, and later on the druid PC can run into some of them (who probably flee down to Seaquen as refugees, and try to start a Chapel of the Aquiline Cross there; they will owe him a huge favor). If the PCs all fall, the druid feels like he dies, then has a vision of an eagle, its wings spread wide like a cross. He awakens in the church that night, completely healed, and with an unerring sense of direction toward Gate Pass.
(The other pseudo-minions might tag along, but ultimately they have other goals to pursue.)
Act Three
The bard has been captured by the inquisitors and tortured. Let him decide what sorts of horrors were inflicted upon him. Now, though, he is chained in a prison wagon along with another captured spellcaster, and they're en route to the far northern reaches of Ragesia. The inquisitor who captured them is off with more important duties (if you want to have fun, make it be Guthwulf), but several guards watch the wagon, and are ready to kill the mages if they cause any trouble.
Meanwhile, the avenger and some like-minded allies have learned the route of this prison wagon, and plan to rescue the captives. As the wagon crosses a bridge in a snow-shrouded forest (a few days' trek from Gate Pass), they spring their ambush.
Extra Cast
- Fellow prisoner. A warlock. He's the 'human sacrifice,' 'kill anyone who looks at you funny,' old-school style warlock. Legit evil.
- Rescue wayfarer. A shielding swordmage who fights with a quarterstaff instead of a sword. He's an apprentice wayfarer, who hasn't learned any of the major teleportation tricks. (Point out that he takes a bit of fire damage when he teleports, but it doesn't count as a hit.)
- Rescue sorcerer. He lays down fire from afar as the others rush in.
Maybe the PCs have a trap set up, so when the wagon reaches the bridge, a log falls across the far side of the bridge, blocking their escape. The PCs are up against, say, four minion guards and one actual guard (just steal stats from Scouring of Gate pass).
Start the encounter with the Ragesian guards harassing them as they go through the woods. One guard pokes them with sticks, and threatens to leave the bleeding on the roadside if they cause any trouble. They approach the bridge, and the lead guard says to the prisoners, 'When you get where you're headed, you'll wish you were back here, just getting poked instead of being in the pit.'
Just then, they trigger the trap, and the ambush starts. Hopefully the PCs win, but if they look like they're about to fail, bolts of fire fly out of the woods and take down the Ragesians. The PCs just happened to have crossed paths with Katrina, and while she's not going to stick around and pick up some deadweight prisoners, she's still conflicted enough that she'd rather help a few mages than let the Ragesians kill them.
I hope some of that is useful.
