Seventy-two guns were stolen from a San Francisco police storage facility. Now murders are spiking. The only connection: all the perps claim the stolen guns were anonymously left for them to do with as they pleased.

Mei Ling, now head of the SFPD's Computer Forensics Team, and newest member of The Rookie Club, sees another connection when a network-hacking device is found installed in the storage facility.

Then bullets start crashing through Mei's home, convincing her she's right. Now Mei just needs to find the hacker before becoming his next murder victim.