There are a total of 26 strangers which appear throughout the course of the game. For this achievement you will need to complete 10 multi-part stranger stories. Strangers which only have a single encounter do not count for this achievement.
Strangers appear on the map as a white dot with a question mark in the middle. Some appear automatically via story progression, whilst others will not appear until you are within a certain distance of their position. The following is a list of all strangers and the chapter which they unlock.
Strangers highlighted in bold will add progression towards this achievement:
The Noblest of Men, and a Woman (Valentine)
All That Glitters (West of Flatneck Station)
The Smell of the Grease Paint (Van Horn Trading Post)
Arcadia for Amateurs (South-east of Strawberry)
Fundraiser (Saint Denis) *
American Dreams (Triggered by finding 3 map pieces)
A Fine Night For It (Triggered by a random encounter in the Bayou at night)
Geology for Beginners [Unlocks 'Rock Carvings' collectables] (North-west of Strawberry)
A Test of Faith [Unlocks 'Dinosaur Bones' collectables] (North-east of Flatneck Station)
Smoking and other Hobbies [Unlocks 'Cigarette Cards' collectables] (Flatneck Station)
He's British, of Course (South of Emerald Ranch)
A Fisher of Fish [Unlocks 'Legendary Fish' collectables] (North side of Flat Iron Lake)
The Iniquities of History (Rhodes)
No Good Deed (Rhodes) ***
Oh, Brother (Valentine)
The Ties That Bind Us (Rhodes)
A Bright Bouncing Boy (Saint Denis)
The Mercies of Knowledge (Saint Denis)
The Artist's Way (Saint Denis)
Help a Brother Out (Saint Denis) **
Duchesses and other Animals [Unlocks 'Exotics' collectables] (Saint Denis)
Idealism and Pragmatism for Beginners (Saint Denis)
The Wisdom of the Elders (West of Van Horn Trading Post)
The Widow of Willard's Rest (Willard's Rest, North-east of the map) *
The Veteran (O' Creagh's Run, North of Emerald Ranch)
The American Inferno, Burnt Out (West of Blackwater)
* missions will be unavailable after chapter 6.
** Also an Honour Mission required for 100% completion.
*** Mulitple reports that this mission counts even though it doesn't fit the criteria!
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