QUESTION: What is plagiarism? If I borrow an author’s style, is that plagiarism?
Plagiarism is a very complex issue. The most obvious example is a writer who has cobbled together many paragraphs of someone else's work with their own words as cement.
A less obvious example is someone who uses someone else's work as a template to their own. Each scene is a rewrite of a scene in someone else's novel.
Another very common form of plagiarism is cutting and pasting text from a nonfiction source into a novel.
Famous writers certainly aren't exempt from being guilty of plagiarism. Janet Dailey's flagrant plagiarism of Nora Roberts' novels is a perfect example. (JD was proven guilty and had to pay restitution.)
Not so famous writers are also found guilty of the same thing. Some years back, a teenaged novelist had her first novel pulled off shelves when readers found that she'd patched together several other books to create her own.
Copying someone’s style isn’t plagiarism as long as you aren’t copying content. Many new writers try to emulate a favorite author’s style because they haven’t found their own yet. After a few years, gained confidence, and the sheer difficulty of maintaining someone else’s voice, most develop their own style.
As a reader, if you feel that the two books are so similar that it might be plagiarism, you should contact the publisher or the author, express your concerns, and let them decide whether this is plagiarism or not.
Most authors have websites with contact information as do publisher websites.