When her domestic partner Susan is brutally murdered, Nicola Tanner is convinced that she was the intended target. The murderer's motive is likely connected to her recent work on a string of cold case honor killings. Despite being placed on leave, Tanner insists on pursuing justice for Susan-and she turns to fellow DI Tom Thorne for help. Agreeing to take the case, Thorne quickly finds that working in such controversial territory among London's Hindu, Muslim, and Sikh communities can be dangerous in more ways than one. But when a young Bangladeshi couple goes missing, Tanner and Thorne must put everything on the line to investigate a case that is anything but cold.