Alex Rider (book 13). Fast-paced action spy series.
Want to start at the beginning of the series? The first book is Stormbreaker.
The protagonist is 14 at the start of the series and although he doesn’t age much between each book, the content gets edgier. A 9 year old could enjoy the first few books, especially if you read aloud to them, but the later books are probably best suited to older middle grade readers.