Miss Morstan was a very attractive young woman, he had to admit. Clever and poised too. She was not conventionally beautiful but that was more than made up by the spirituality of her face and her strength of character that came through so clearly in that first interview. He wondered if she might accept his advances, once she ceased to be a client.
The danger was that she might see him as only a treasure-seeker, not realizing the real treasure to him was the woman herself.
Then there was little matter that Watson was clearly in love with her already.