Niamh and Ruairidh Macfarlane co-own the Hebridean company Ranish Tweed. On a business trip to Paris to promote their luxury brand, Niamh learns of Ruairidh's affair, and then looks on as he and his lover are killed by a car bomb. She returns home to Lewis, bereft. I'll always be there for you. Niamh begins to look back on her life with Ruairidh, desperate to identify anyone who may have held a grudge against him. The French police, meanwhile, have ruled out terrorism, and ruled in murder - and sent Detective Sylvie Braque to shadow their prime suspect: Niamh. I'll keep you safe, no matter what. As one woman works back through her memories, and the other moves forward with her investigation, the two draw ever closer to a deadly enemy with their own, murderous, designs.