When there is tension between two people, it's not uncommon for them to triangulate, to involve another person in order to diffuse the tension. Let's explore the triangles in this novel.
One place to begin with Lydia/Portia/Olivier. Any thoughts o how Lydia, at the novel's end, tells Katie what he's about yet she has not anything to extricate her flesh-and-blood daughter from his clutches.