I took out the mutant leader queen in chains, since she seemed poorly thought out. I made Zul out to be much more manipulative and Tzeentch like. After the battle at the end of chains, Zul possesses the dead interrogators body.
He naviagtes them out of the warp and into the screaming vortex. The Chains emerges close to orbit around Sacgrave. They saw the ship mentioned in the BC book that orbits the planet. Their ship is basically unable to move at this point, but still has shuttles. Zul at this point claims to know the ship orbiting Sacgrave. They have a "history" together.
I turned that ship into a daemon ship that the players could take control of.
Zul offers them a compact to get into the ship and perform a ritual to bring him on board. (I am making compacts in my game rituals that are partially binding to the Chaos Gods, which is why failing them gives corruption.)
[I took this as an oppurtunity to introduce compacts to the players, explaining them out of game and tying them into fluff ingame. I also brought up that if a player has a personal goal they want to add, to just text me with what they want to do. Two players texted me that they wanted to possess the Cord personally. ]
To do this, Zul says they need an artifact that allows partial control over some Daemons, called the Tyrants Cord. He can sense that the Cord lies on the surface of the planet. they can scan the location to somewhere in the Zigguraut in the Weeping Chambers on the planet below.
The players agree to the compact and went down to the planet. They go through the GM kit adventure, with the other party more being in the background. Instead, they already knew about the Zigguraut and had to do investigation to find out how to get there. After doing a bunch of the stuff in the GM kit, they reach the Zigguraut, and find that the Cord was recently taken by the group of outworlders in the kit. They chase them down and kill them, getting the Cord.
After getting the cord, they shuttled up to the Daemon ship. They get on board, and navigate through a maze like messed up daemon ship. The cord is briefly glowing at this point, its powers helping to protect the players from the Daemon. The tech priest wants to interface with some Cogitators to get a layout of the ship so they can actually have an idea of where the hell they are supposed to go. However, intelligently; she realizes that interfacing with a Daemon ship is a bad idea unless she is wearing the Cord.(she also had a personal goal of getting the cord for herself ).
She explains to the party to give her the Cord so that she can access the Cogitator. However: The current player wielding the cord was the other one who claimed it as his personal objective.
A little tussle ensues (in which the current Cord weilder got messed up bad), leading to the Tech Priest and another player gaining control of the Cord from the one who was weilding it. She puts the Cord on, and interfaces with the ship. as she does this, the Cord starts to glow very brightly and in her mind the Daemon starts talking to her. She gets ship information and agrees to meet the heart of the Daemon ship in the bridge. (that is hwere the ritual to summon Zul needed to happen) The players make their way to the bridge, minus the player who previously held the Cord who was doing his own thing.
They got to the bridge and saw the pulsating heart of the ship. The daemon now talks to all of them: promising to help them burn the starts to the ground if they repaired it's engines and let it sail the void again. The players begin talking with the Daemon, but mention summoning zul on board. The ship vehemently disagrees with this, but will allow them to bring Zul on board if they betray him and eliminate him.
The players at this point had the choice of allying with Zul or the ship. They conduct the ritual to bring Zul on board, but add some binding runes to the summon. Zul arrives on board, and asks the players to hand over the Cord so that he may prepare to take over the ship and get things going. The players proceed to turn on him: Zul rages but is defeated by the players with the help of the Daemon Ship. Before he dies, he reaches out mentally to the other player still wandering the ship and makes a bargain of vengeance with him. They know have a link and mutual desire to see the one player currently using the Cord broken.
This all ends with the players in control of the Daemon ship, having made an impression in the weeping halls below, and ready to go off and do whatever they want. They are now prepared to enter into a compact with the daemon ship and go get their death and destruction on.
Sorry for any typos, I am pressed for time.