Here is a video walkthrough of this chapter:
Credit to TwoFiveFiveMike.
Here is a step by step on how to get through Chapter 3:
Meet with the trader and end up getting scammed.
Talk to the various people as you make your way through Endercon.
Retreive Ruben from the butcher.
Talk to the Usher.
Talk to the lady selling slime to collect eight pieces of slime.
Talk to Lukas to get your ninth piece of slime.
Craft a slime block.
Break the glass and release the chickens.
Pull the lever in the library.
Follow the action commands to escape.
Decide whether to help Lukas or talk to Gabriel.
Escape Endecon and head to the temple.
Open the portal.
Pick to save either Gabriel or Petra.
Enter the portal.
Credit to IGN. Once you enter the portal, a cut scene should roll out and the achievement should pop moments later. If it does not for some reason, it will come up at the start of the next chapter.