Years ago, LAPD detective Michael Gideon and his German shepherd K-9 partner, Sirius, walked through fire to save Los Angeles from serial killer Ellis Haines, known as the Weatherman. Now, they prepare for a final showdown with their mortal foe.

It's been a year of change for Gideon and Sirius. Both are new parents, but for the two of them, the joys of fatherhood have to wait. After a few months of silence, the All-In Killer has begun his murderous spree again—and his latest victim died only miles from Gideon's doorstep. The All-In Killer has made it no secret that his homicidal countdown will end only with the deaths of Gideon and Sirius. When Gideon decides he can no longer hide the encroaching threat from his wife, they prepare together for the approaching storm.

While Gideon chases down a new lead that might prove his suspicion that the All-In Killer has been communicating with Ellis Haines, an ecoterrorist bomber strikes California, and a recently retired deputy US marshal and her bomb-sniffing dog go missing. Gideon and Sirius join in that manhunt, doing what they do best—saving lives.