The Following opens up with a cutscene that sends our hero, Crane, on a hunt for people immune to the zombie infection out in the countryside of Harran. When the scene ends, you will be in control in a sewer. The path is straight forward and leads outside.
On the cliffs, follow the ledges along the wall and climb your way out the the high point in the center of the rocks. Dive from the top into the clear water below. Swim to shore and pass the decorated shrine by taking the path to the left. Unlocked Grapple Hook in main game can make this trip much faster.
Not far past the shrine, on the right hand side of the path, is a Hunter’s Tower. Climb in it and pick the locked box to find the blueprints for the Flame Stabber.