Without Fail by Lee Child

Jack Reacher walks alone.

No job, no ID, no last known address. But he never turns down a plea for help. Now a woman tracks him down. A woman serving at the very heart of US power. A woman who needs Reacher's assistance in her new job.

Her job?

Protecting the Vice-President of the United States.

Her problem?

Someone wants the VP dead.

Although the Jack Reacher novels can be read in any order, Without Fail is the 6th in the series.