Throughout the book this author uses the present tense, and that's fine (Although a lot of novels use the past tense, some use the present as this one) Now, what's perplexing me is she uses the past perfect without a point of reference in the past. I think she should use the simple past. I know there are a few other ways you can use the past perfect, but this one doesn't seem to meet the conditions. Do you think there is any rhetoric effect she is attempting?
He pities his parents when they speak to him this way, for having no experience of being young and in love. He suspects that they are secretly glad when Ruth goes away to Oxford for a semester. She'd mentioned her interest in going there long ago, in the first weeks of their courtship, when the spring of junior year had felt like a remote speck on the horizon. She'd asked him if he minded if she applied, and though the idea of her being so far had made him queasy he'd said no, of course not, that twelve weeks go like that. (The Namesake by Jhumpa Lahiri)
'Long time ago' modifies 'had mentioned,' right? What is the point of reference for 'had mentioned,' for instance? In other words, there should be the verb in the past tense that acts as a point of reference for 'had mentioned,' or at least something that covertly tells your intuition the point of reference. 'Long time ago' does not acts as the point of reference, I don't think, because it is only there to give you information on when she 'mentioned' her interest in going there. I've presumed this use of the present plus the past perfect throughout is her style. What do you think? From the beginning to the end, it's only 80% the present, and 20% the past perfect, and none other.
Sometimes writers use Past Pefect just to emphasize that event took place a very long time ago and there should not necessary be the "reference point" such as a "simple past" verb if I can say so.
HSS've presumed this use of the present plus the past perfect throughout is her style.
It's quite true.

Nevertheless, I wouldn't use it and Michael Swan's book supports me:

"The past perfect is not used simply to describe something that happened some time ago or to give a past reason for a present situation".
I agree with Fandorin; this is poor usage. I noticed it at a scattered points in the novel and it irritated me. Otherwise it's a beautifully written book. I can understand why she chose to write it in the present tense, but it just gets too clunky at times.