Following the discovery of Catriona's body holding his sister's doll Magnus is taken into custody though it is clear he did not murder Catherine whilst Catriona's death is shown to have been an accident. Catriona's brother arrives on the island and tells Perez that when they were children their father was having an affair. The other woman turns out to be Sally's austere mother Margaret, the teacher, and she admits that Catriona saw her with her lover before running off. Magnus was aware of this. It transpires that Catherine was filming interviews with local residents for her project and the discovery of her phone shows an argument with her apparent killer. When this person is tracked down it leads the police to the actual culprit.
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