My dad's birthday is in a few days, and I'm looking to get him a few books. He's a fan of spy novels like Ken Follet's Triple and Alex Berenson's The Faithful Spy. Unfortunately, the only spy novels I've read were recommended by him, so I need some recommendations. I don't know everything he's read, but I know that he recently read a novel by Daniel Silva and enjoyed it up until the end, which he found to be enough of a let down that he's not interested in more Silva novels. Providing it's not super obvious, though, I think it's a safe bet.