A strong start - but where is it headed? - Javier Marias's The Infatuations

Been meaning to read Javier Marias for some time and yesterday started reading his most recent novel, The Infatuations, and am impressed through first 100 pages or so and wondering how - and if - this novel will take shape and develop. Marias gets you engaged right from the first sentence, as his first-person narrator, a low-ranking books editor whose career involves dealing with cantankerous and narcissistic authors, notes that the last time she saw Miguel was when he left the cafe - he was murdered minutes later. The entire novel, to this point, has involved her recounting how she used to watch a man named Miguel and his wife, Luisa, at this cafe every morning - she dubbed them "the perfect couple" - but never spoke to them or knew anything about their lives - then learned from news accounts that he had been stabbed to death by a deranged, homeless man. Later, when she sees Luisa in the cafe, she introduces herself; L. invites her to her apartment for conversation, and, in most European fashion (Marias is a Spanish novelist, this one set in Madrid) they discuss matters of life and death and recovery. The novel moves along very easily, and we, like the narrator, are certainly curious about this couple. At the 100-page point, however, the quality of this novel will depend on whether Marias will deepen the mystery, gradually reveal new information that will make us see the couple - and our world - in a new light. Was it really just a random crime, for example, or was there some motive that we will later learn? Is the narrator as reliable as she seems, or is she holding something back from us? Will her involvement with Luisa somehow change the nature of the "facts" of the novel, in the way in which human interference is inevitable in any scientific experiment or observation?