I think it was more of an overwhelming memory sparked by the smell of the bath products rather than an actual apparition. I didn't buy why the protagonist would leave, why the husband would suspect him and why he would disappear.
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(view spoiler)[I had exactly that reaction. It was a plot that belonged to another book, I though. I see that he's trying to tie guilt and grief together, but opening up that whole business about Lucy just didn't work for me. (hide spoiler)]