Agatha Christie - Hercule Poirot: The First Cases

Story-related; cannot be missed.

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

Walk through the snow and into the house in the upper right corner. The big foyer you enter is called the Great Hall.

Great Hall
Look at the guest book on the table directly in front of you
Interact with the two doors on the left side (Salon on the left and Dining Room on the right)
Talk to Zakariya
Go upstairs

First Floor Hall
Look at the receipt on the table to the left
Look at the three paintings on the left wall
Enter Jackie's Bedroom (second door on the left wall; only one unlocked)

Jackie's Bedroom
Look at the changing screen
Look at the window
Look a the perfume bottles

Mind Map - Locate Your Room
"Very few staff working" + "Archibald is stressed"
"Locked dining room door" + "Locked salon door"
"Rooms for tonight's event" + "Staff are very busy"
"Perfume bottles" + "Changing screen"
"Room prepared for female guest" + "Archibald stressed due to lack of staff"

Jackie's Bedroom
Look at the pillow on the bed
Exit out of the bedroom

First Floor Hall
Talk to Gedeon
Go back downstairs

Great Hall
Talk to Zakariya
Talk to Angeline
Look at the  pen inside the glass case in the back against the left wall
Look at the tag on the vase over on the right side at the hallway
Look at the painting on the wall in this right side hallway
Enter the first door in this hallway, for the Butler's Pantry

Butler's Pantry
Talk to Elizabeth
Look at the cupboard
Look at the pots and pans
Interact with the door you came in
Look at the letter next to the pots and pans

Mind Map - Locate Your Room
"Group of saints" + "Plaques above doors"
"Seven saints assigned to rooms" + "Guests residing on first floor"
"One door missing" + "Zakariya says..."

Mind Map - Blackmail Letters
"Handwritten" + "Quill pen"

Butler's Pantry
Talk to Elizabeth
Look at the deeds next to the broom
Exit back out to the hallway

Great Hall
Talk to Angeline
Talk to Zakariya

Mind Map - Van den Bosch Family
"Luc passed away" + "Elizabeth hasn't been herself"
"Elizabeth mourns..." + "Elizabeth upset Florette was dismissed"
"Tag on vase" + "Receipt"

Mind Map - Blackmail Letters
"Staff concerned..." + "Madame unaware..."

Great Hall
Go upstairs

First Floor Hall
Talk to Gedeon
Go to the hallway off to the right and take the upper door to the Northeast Quarter

Northeast Quarter
Look at the luggage
Look at the plant in the corner
Interact with the door on the right
Exit back to the hallway
Enter the lower door to the Southeast Quarter

Southeast Quarter
Look at the luggage
Look at the plant in the corner

Mind Map - Van den Bosch Family
"Angeline mindful" + "Angeline guilty"
"Angeline is trying..." + "Angeline tried..."
"Gedeon believes..." + "Family keeping up appearance"

Southeast Quarter
Enter the door on the left to Poirot's Room

Poirot's Room
Look at the book on the vanity
Look at the window
Look at the fireplace
Talk to Elizabeth (she'll have entered the room)

Mind Map - Blackmail Letters
"House deeds" + "Blackmailer wishes family to leave"
"House holds many secrets" + "Staff aware of blackmail"

Poirot's Room
Talk to Elizabeth
The Blackmail (25G) unlocks