The show begins with a drug deal being conducted between the American Mafia and the Japanese Yakuza. However, there's a hitch--during this deal, some of the guards realize that one of them is a cop and he's murdered. Soon, the body is identified as Michael Morishima--a cop and friend of Sam's. Based on a trend I've noticed in "Quincy", the only time you'll see Sam's friends or family is when one of them is murdered--sort of like when Quincy goes on vacation, some unsolved murder or death comes up to distract him.
In investigating the death, Quincy and Sam noticed the man was stabbed. However, the wound is VERY clean and atypical of the usual stabbing. Sam realizes it's because it comes from a Japanese sword--a single-edged but extremely sharp blade. This and a meeting with a special agent working on Japanese organized crime lead them to the Yakuza.
Unfortunately, during this investigation, the dead man's father (Mako) investigates the crime on his own and vows revenge. Eventually, however, the killers learn about him and set a trap for him. Now here is where it gets a little silly, when Sam learns about this, he, too, goes off like some sort of lone wolf instead of working within the system (just like the last time a family member was killed!). Overall, entertaining but highly improbable.
By the way, even though the Los Angeles Police Department has thousands of cops, why is it that Monahan and Brill come to the rescue at the end?! What are the odds?