The Yellow Serum

{Set 3 years after Tris' death, 6 months after the timeskip.} Tobias still misses Tris, but one day, Caleb offers him the opportunity of see her again... and to maintain a promise he made to her. (No, this in not a "Tris is miraculously revived/still alive" story!) [Tobias' POV. Three-shot. Chapter 1-2 rated T for slight swearing and themes, chapter 3 ratem M for heavy themes.]