Lethal Legacy by Linda Fairstein.
The most recent Alex Cooper novel was particularly resonant for me: it deals with books and libraries, but we don't discover this until a few chapters into the story.
A refresher: Alex is an ADA attached to the NYPD sex crimes unit. She works primarily with Detective Mike Chapman, who just might harbour an unrequited love for her.
Alex and Mike are summoned to an apartment building on Manhattan's Upper East Side by a resident who fears that his neighbour may have been assaulted. But the young woman, Tina Barr, refuses to co-operate. The next day, a dead body is found in Tina's apartment, and Tina has disappeared. Then the investigators learn that Tina is a freelance rare book conservator who once worked at the New York Public Library.
A jewel-encrusted prayer book is found with the body, who turns out to be the assistant of heiress Minerva Hunt, whose wealthy family have a collection of rare books and maps, some of which have been donated to the Library. It's at this point that the plot becomes a bit serpentine: Alex's crew suddenly need to find an old map which will give them a clue to the identity of the murderer. Their search leads them to interview book experts, old and young, rich and poor, honest and deceitful.
There's a lot of interesting information here about the New York Public Library, about rare books and maps, about their history, conservation and storage. Fairstein's research is, as usual, impeccable.
To a bibliophile like me, this story was fascinating, but I recommend it not only to other bibliophiles, but mystery and thriller lovers as well.