Question of the Week

What book has led you to another book?  I'm thinking of the time that I read a novel about a fictitious daughter of Wallis Warfield Simpson (THAT woman) and Edward VIII.  Emerald by Elisabeth Luard, which is sadly no longer in print.  From there I went to biographies of Wallis and Windsor and finally to the auction catalog of their home after they died.  I obsessed, I think.  So, has this happened to you?  Where did you start and where did you end?