De Pauli and Jo go undercover at a nightclub in the hope of securing evidence against O'Brien (Patrick O'Kane), a known drug dealer with a history of violence. When De Pauli's cover is blown, the operation is aborted, much to the dismay of Tomaszewski, an out-of-town detective who finally hoped to bring O'Brien to justice with the squad's help. The situation turns from bad to worse when O'Brien manages to obtain Pauli's address, and leaves a threatening note on her front door. Cally and Frank decide to pay O'Brien a visit, but their incitement only leads to further intimidation. When Julie finds out, she is disgusted and warns Cally to stay away. Meanwhile, Sullivan tries to use Cally to help patch up his marriage, but Sue rebuffs him, and reveals that she has fallen in love with another man. When O'Brien issues another threat, De Pauli decides to seek refuge in a police hostel, but not before she and Cally come to blows - and end up kissing each other. Meanwhile, Pauli is furious to ...