Who's on First is the third in the Blackford Oakes series by William F. Buckley. It has dropped to $1.99 at Kindle and Kobo US (couponable/VIPable). Much as with Ruth Dudley Edwards (and not, for some reason, with Tom Clancy, IMO), although I don't agree with the author's politics, the stories are still fun, and the politics doesn't seem to extraneously get in the way but rather to be a reasonable part of the story. YMMV... Anyway, I've enjoyed the Blackie Oakes titles that I've read.
Kindle US:
https://www.amazon.com/gp/product/B0116EBXO0
Kobo US:
https://www.kobo.com/us/en/ebook/who-s-on-first-2