Agatha Christie - Hercule Poirot: The First Cases

This achievement spans the entire game, and as the description says, requires you to meet (i.e. talk to) every character in the game. The good news is that, in my experience, every single character is story-related and unmissable. However, to be safe, I have listed all characters below, and what chapters they are first available in. The list is therefore in the order of when you can first talk to each character.

If you follow this list, you should unlock this achievement in Chapter 5, as soon as you talk to Rehana in the Kitchen (but you will also talk to her unavoidably after that).

Prologue
 

1. Elizabeth
2. Cassandra
3. Angeline
4. Florette

Main Game
 

1. Zakariya - Chapter 1
2. Gedeon - Chapter 1
3. Angeline - Chapter 1
4. Major - Chapter 2
5. Archibald - Chapter 2
6. Margeux - Chapter 2
7. Inge - Chapter 2
8. Jackie - Chapter 2
9. Hugo - Chapter 2
10. Ernesto - Chapter 2
11. Rehana - Chapter 5