Agatha Christie - Hercule Poirot: The First Cases

Story-related; cannot be missed.

Here is a walkthrough of the chapter, including everything needed for achievements.

Poirot's Room
Leave the room, then exit back to the Main Hall First Floor
After the cutscene, enter the double doors to the Library

Library
Talk to Hugo - Curious, Direct, Honest
Hugo Beckers (25G) unlocks
Leave the Library
Go downstairs
Walk down the hallway all the way to the end on the right and enter the door to Staff Quarters

Staff Quarters
Look at the logs
Look at the newspaper
Look at the hammock
Look at the cupboard
Look at the luggage
Look at the clothes hanging between the two bunkbeds
Work-life balance (15G) unlocks
You will automatically be taken to the Butler's Pantry

Mind Map - Archibald and Rehana
"Rehana claims..." + "Archibald staged..."
"Major's coat..." + "Hugo saw the Major"

Butler's Pantry
Talk to Archibald
Talk to Inge
Talk to Rehana

Mind Map - Archibald and Rehana
"Worn out boots" + "Madame pays staff..."
"Staff member's boots" + "Someone else wore Major's coat"
"Rehana unsure..." + "Archibald forgot..."
"Archibald and Rehana unsure..." + "Staff covering for real time of death"
"Archibald and Rehana fabricated..." + "Staff member impersonated..."
"Staff are hiding..." + "Staff may be involved"

Mind Map - Association
"Inge feels disconnected" + "Staff are involved"
"Elizabeth mourns..." + "Rehana distraught"
"Elizabeth looked white" + "Staff are involved"
"Elizabeth found body" + "Rehana helped Elizabeth"
"Rehana wasn't seen" + "Staff member impersonated..."
"Rehana wasn't seen" + "Archibald staged..."
"Archibald was covering..." + "Elizabeth found the body"

Mind Map - Investigate the Murder
"Rehana was covering..." + "Archibald staged"

The Family (50G) unlocks after some cutscenes