Nash and Joe are on the trail of two brothers, heirs to a big Mafia family, which is complicated by the fact that Kelly used to be involved with one of them.

After a nearly 20 year absence, the notorious San Francisco serial killer, ""Zodiac,"" returns to taunt Nash as well as haunt Nash's mentor (who has since retired). But is it the actual Zodiac, or just a lethal copycat? Meanwhile, Joe goes undercover as a bike messenger to nab a free wheeling drug dealer.