A young woman's paternity test leads to the reopening of a notorious cuddle case from the seedy underworld of 1980s Soho in which the prime suspect was mysterious ex-jazz chanteuse Angela Gold. Meanwhile in UCOS, feathers are ruffled when recently retired police officer Dan Griffin joins the team.
New Tricks follows the work of the Metropolitan Police Service's Unsolved Crime and Open Case Squad (UCOS). Led by Detective Superintendent Sandra Pullman, it is made up of retired police officers who have been recruited to reinvestigate unsolved crimes.
The series title is taken from the popular expression "You can't teach an old dog new tricks". The "old dogs" are successful in adapting their skills and experience to modern policing, with their knowledge of past cases proving especially useful.