In the fourth season premiere, Griffith Park is a blazing inferno, threatening sections of Los Angeles, Glendale, Burbank and San Mateo. With four people dead and firefighters desperately trying to keep the flames at bay, the Priority Homicide Division is called in to begin an investigation. Things turn ugly when an old nemesis of Brenda's -- pyromaniac Bill Croelick (guest star Jason O'Mara "Life on Mars," "Grey's Anatomy," "Men in Trees") -- enters the scene. To make matters worse, a reporter has been attached to the squad as part of a PR campaign for the LAPD. On the home front, Fritz and Brenda have moved into a duplex, but the owner doesn't allow pets. This doesn't stop Brenda, however, from doing everything she can to keep Kitty under wraps, even if it means fighting with Fritz over the situation.