This season, the men and women of the 15th find themselves under pressure from within, as Internal Affairs investigates Det. John Clark (Mark-Paul Gosselaar) when his name turns up in a murdered prostitute's little black book. Outside the station house, Connie McDowell's (Charlotte Ross) developing relationship with Andy Sipowicz (Dennis Franz) uncovers new challenges. Sipowicz strains to maintain his personal life and clear Clark's name... but to do the latter, he'll need to call on an old friend: Detective Diane Russell (a guest starring Kim Delaney, reprising her Emmy award winning role.)