The final instalment of the Infernal Affairs Trilogy is set both directly after the events of the first film as well as in the months leading up to them, introduces two new characters and fleshes out the part played by psychoanalyst Kelly Chen.
The timeline jumps back and forth repeatedly which can make the narrative seem a little confused as Yan’s character makes an appearance even after his death as Lau’s mental state deteriorates. Unfortunately it is this plot development that leads the trilogy into unconvincing melodrama as his schizophrenia seems very contrived and gimmicky. The scenes set earlier in the erratic timeline are better but they don’t really add anything to the original story making part III seem like it is making excuses for its own existence.
The film is still well directed and performed and is certainly not a complete waste of time, but it feels more like a tacked on addendum rather than a natural continuation of the Infernal Affairs story.