Massively confused about the plot

... the gist that i got was that a group of cops had orchestrated a complex plot involving a bombing, some hostages and ransom to remove Deputy Commissioner Lau and to have Deputy Commissioner Lee promoted to Commissioner. Apparently, there was some internal frustrations over Lau's budget cuts and preferred Lee's hardline tactics instead.

Same here. What if Sean Lau hasn't taken over the operation, and his father was still on the case? Anyway... I have to agree that this movie is flawed and doesn't make a lot of sense.