Liverpool 1 focused on Detective Constable Isobel De Pauli (Samantha Janus), a successful Metropolitan Police detective. Her partner's career move to Liverpool in turn sees De Pauli transferred there. Upon arrival she is partnered with introverted DC Mark Callaghan (Mark Womack), a no-nonsense officer brought up on the streets of the city he now polices; the opening sequence of the first episode culminates in Callaghan throwing a suspect from an apartment window.
The earlier episodes centre around the dual themes of the personality clash between De Pauli and Callaghan, coupled with the ongoing saga of the squad's pursuit of local gangster John Sullivan (played by Paul Usher). Callaghan's relationship with Sullivan - who is his cousin - and the interconnectedness of the city, are themes throughout the series
Series 1 - Episode 1 - DC Isobel de Pauli is transferred to the vice squad at Bridewell, Liverpool 1. Her new partner, DC Mark Callaghan, is in court for the trial of drug dealer Mikey Sullivan. De Pauli and Callaghan follow up an incident where a man was thrown from a balcony, but the victim refuses to cooperate. The squad is called to a disturbance at a club owned by a major drug supplier.
Series 1 - Episode 2 - DC Callaghan and de Pauli try to trace a young girl with a conviction for prostitution who has gone missing. Both officers are interrogated about the abortive arrest of Mikey Sullivan.
Series 1 - Episode 3 - DC Callaghan and de Pauli interview a convicted paedophile in connection with the disappearance of a young boy. Callaghan is appalled to learn that local drugs baron Sullivan has put money into his brother's new bar.
Series 1 - Episode 4 - DC de Pauli investigates a case of petty violence and is drawn into John Sullivan's the gangland past.
Series 1 - Episode 5 - The vice squad investigates the murder of a prostitute. DCs Callaghan and de Pauli find their private lives dragged into the station.
Series 1 - Episode 6 - A surveillance operation is threatened, and DC de Pauli is forced to choose between the job and her fiancé.
Series 2 - Episode 1 - DC Callaghan and de Pauli investigate the reported murder of a prostitute by her pimp.
Series 2 - Episode 2 - DCs de Pauli and Callaghan investigate a music teacher accused of child abuse by an 11-year-old pupil.
Series 2 - Episode 3 - DC de Pauli and Acting DS McMullen go undercover at a club to uncover some drug dealers.
Series 2 - Episode 4 - A fresh supply of uncut heroin has hit the streets, but the squad is told to raid a massage parlour.
Series 2 - Episode 5 - The squad investigates the source of a new batch of uncut heroin following four drug-related deaths in the city.
Series 2 - Episode 6 - DCs Callaghan and de Pauli investigate the shooting of a bouncer outside a nightclub.