The Fifth Profession by David Morrell

Savage, a former Navy Seal, and Akira, a modern-day Samurai, are now both protectors, high-quality bodyguards. But both of them have to deal with a memory of seeing the other die when someone killed their client. In a world where nothing is as it seems and hired killers stalk their every move, you can’t trust yourself, let alone anyone else.

As expected with a Morrell story, this is action-packed with twists that you never see coming. Hang on to your seat!