This book is another in the Matt Helm series, the fourth (I think).
In it, Helm travels to Mexico, gets some secret information, and then walks into a trap on purpose to get to an agent known as The Cowboy who might be sabotaging a nuclear test. When he gets caught, as planned, Helm turns the tables on his captors and on the woman who has double-crossed him–as planned–even as they’ve fallen in love.
It’s not very complicated, but it’s a 60s paperback adventure. You get a handful of scenes, a female love interest of potentially duplicitious motivation, and then you get a sudden climax with a big explosion. A hundred and fifty pages, and you’re done. Man, I love these paperbacks.