Assassin Zero (An Agent Zero Spy Thriller—Book #7) by Jack Mars

When a mysterious ultrasonic weapon attack may be the preamble to something greater, Agent Zero sets off on a global manhunt to stop the ultimate devastation before it is too late. Agent Zero, trying to come up for air on the heels of the President’s impeachment and Sarah’s close brush with danger, wants to retire from the service and try to get his family back together. But fate has other choices for him. With the safety of the world at stake, Zero knows he must follow the call to duty. Yet his memories are shifting, and with it, new secrets are flooding back. Tormented, at his low point, Agent Zero may be able to save the world—but he may not be able to escape from himself.