The special picks from this moment and follows as if nothing had happened and there had not been more than three years (for the viewer) between both moments. Which, if you see all together will not matter, but if you see this special without refreshing your memory, well, you will have problems trying to remember why the two characters had ended up there.
Without getting into what happens between them both, the special then follows your typical "Border" episode, with a 'ghost' asking Ishikawa for help, and him trying to decide which way to go: the 'official' one, with rules, police and the system, or the 'un-official' one. The special does a great job on keeping Ishikawa on the grey zone (more than ever), without letting us know if he will go all dark, or if he will keep trying to fight his demons. It helps that Oguri seems to have been born for this kind of ambivalent characters, and that the mood, the pace, and the grey and dark illumination is perfect. From the moment the music from the series sounds, you will be back to the world of Ishikawa, the policeman that, after getting injured and left with a bullet in his head, can talk to the dead.
A really good ending (?; it leaves the door open for a second series or even a movie) to the series, one that fans of the TV series will enjoy.