This achievement can be acquired during the first case Prey Tell.
During this case, you will impersonate the young Wiggins, following a man as commanded by Sherlock.
There will be some obstacles along the way, of course.
First, every time that we will a exclamation point over the head of your target, go to a cover and don't move until the exclamation point is gone. Otherwise, the meter will start to fill and you don't want that.
Then, you will cross some policeman. Go to the street on your left and sprint (with RT) to not lose him.
By the way, if the question mark goes red, it's that you are too close.
After the policeman, you will cross the path of two kids who seem to not to like the young Wiggins, so you have to avoid them by entering the house on your right (the door is open).
Here, you have to interact with man then the fireplace to play a mini-game. You have to clean the fireplace by moving the brush. Be careful, there is a time limit as you get poisoned by the smoke so get out of this fireplace as quick as you can. You can fail this, it won't matter for the achievement.
You are now on the roofs. Follow the path then you soon will be back on the streets.
After a little while, Wiggins suggest to go by the gardens. Do as such. On the first garden, interact with the box to cross the fence then with the two holes.
Then, you will perform a shoe-shiner mini-game and you failed, it will filled by 3/4 the meter.
To succeed, you have to use first the yellow rag on the shoethen the little brush on the wax then use it on the shoe then use the large brush on the shoe then take the white rag.
This the final part: the man is talking to another man, next to a carriage and two dogs. To avoid the dogs, go to the left then, after the cutscene, tap A to get to the carriage.
After the cutscene, if the meter was never full, you will get the achievement.