Emily had been Blaise's lover for about nine years, and from this relationship came Luca. Blaise has failed to father to the boy, and this has had a profound negative impact on him. Always very smart for his age, Luca soon realized his father didn't love him. He became more aware of his constant abscences, but eventually stopped asking where "Daddy" was going". He is angry with Blaise and Emily, and hardly speaks to her--never spoke to Blaise; he never paid attention to Luca either. The only evidence Emily has to assure her Luca is still "alright" is he speaks to her room mate, C. Pinn. This is how I.Murdoch tells it:

"Luca lived in Emily's consciousness as a ceaseless msterious dark pain. When he was a small child she had loved him with an obsessive violence, hardly able to stop touching him, holding him, hugging him. They had lived like animals nestled together in a hole. She loved him in this way still, perhaps even more; but at some strange and awful moment, perhaps two, perhaps even three years ago, as dawning consciousness filled his eyes with puzzlement, he had begun to withdraw from her. He pulled himself away from her embraces. His chattering ceased. He also cried more rarely. Now, and Emily simply dared not think about this, it was so appalling, he hardly spoke to her at all. Sometimes it was as if he had actually become dumb." (p.61).

Luca, along with David, is the first character introduced in the novel, which opens up with an account of the encounter between the two: Luca and his father's "other son". It says like this: "The boy was there again this evening, and the dogs were not barking." David sees him, and describes how "the boy was standing under the acacia tree, just on the near-side of the fence that divided the Hood House garden from the orchard... The boy was staring at the house." David doesn't yet know who this mysterious boy might be, nor what he might be doing there. We don't know either, and are not allowed to find out until much later. Of this mysterious boy we are only told he was "a small figure, a small boy, eight or nine years old perhaps."

Chapter two begins pretty much in the same way as the first: "Harriet Gavender had also seen the boy; only in her case it was the first sighting. And she too had noticed the silence of the dogs... She had seen the small perfectly motionless figure standing just beside the fence of Monty's orchard, merged almost into the dark trunk of the acacia tree."

The boy's identity, which we may by this point have suspected already, is finally revealed when Emily tells Blaise how Luca said he had been to "Daddy's other home". Luca had sneaked into his car and followed him. Now he knows all about his father, his other wife, and his other son. He has been to their home and has seen them. They saw him too, though they do not yet know who he is.