Flack is devastated when his girlfriend, , is shot and killed in the season five finale (episode 5.25, "Pay Up"). His grief over her murder causes him to shoot her killer when he finds the man alone. The shooting is never questioned, but his grooming and appearance suffer. In season six he shows up to work in sweatshirts and jeans, as opposed to his usual suits, dress shirts, and ties; and Stella notices that he has stopped shaving. When Cliff, Angell's father, runs into him at the station one day, he comments that he hadn't seen Flack since Angell's funeral. Cliff invites Flack over to his home for dinner on what would have been Jessica's birthday. Flack accepts the invitation, but is unable to let himself join the festivities; after sitting in his car outside the Angell home for a while, he drives away without anyone in the house knowing that he had been there (episode 6.03, "Lat 40° 47' N/Long 73° 58' W"). Flack spirals down yet further, drinking and missing work. It takes an unexpected rescue by one of his old informants while Flack is intoxicated to begin to bring him to his senses (episode 6.08, "Cuckoo's Nest"). Later episodes show him back in command of himself, as sharp as ever, much to the relief of his friends and colleagues.