New Tricks is a British procedural comedy-drama that follows the work of the fictional Unsolved Crime and Open Case Squad (UCOS) of the Metropolitan Police Service. Originally led by DSI Sandra Pullman, it is made up of retired police officers recruited to reinvestigate unsolved crimes. There have been cast changes, but the squad always consists of three men with a female boss. The series title is taken from the proverb "You can't teach an old dog new tricks".