Case 3 Infamy - Monastery
This achievement unlocks after Holmes follows a captured Orson Wilde to the Monastery.
The goal is to sneak past several guards unseen and rescue Wilde.
Press RB whenever you are in cover, to watch guard movements. If you have alerted a guard the indicator will turn yellow, if the guard has seen you it will turn red. In this case you must quickly attempt to escape.
There is not one set route, there are lots of ways you can go. The first sequence is simple. Just be patient and slowly move forwards. (Ignore metal gates) ,make your way to the river side. You will soon come to a stagecoach. Analyse the scene, noting the scratches on the seats, the bloodstains and the broken windows.
Move onwards into the building. Stage 2 of the sneaking (more complicated)
Wait for the first guard, follow behind him then duck to the left into cover, wait for him to turn around then move ahead. Look for and Climb up a ladder - turn right then drop down. Wait for the guard then move to the right (you can interact with an object) . You will see two guards standing in front of the gate. Look out for a gong to the left, bang the gong to create a distraction. To the left of the gong is a ladder, climb up walk to the end and drop down, make a dash for the doors.
The achievement pops after the cutscene
EDIT: According to comments, if the indicator turns red, As long as you escape and complete the sequence the achievement will unlock, DO NOT skip any part of the sequence as this will void the achievement.