Untraceable by Beth D. Carter

Mae Sawyer has a huge crush on her boss, JD Harlan, but he doesn’t even know she exists. She blends into the background of her data entry job, living for glimpses of him walking through the office. Then one night, everything changes. While working late, she’s caught up in a plot to kidnap him … and gets taken as well.
They wake up in an underground bunker. No electricity. No way to be traced. Alone, they have to rely on each other to stay strong until their captor decides their fate. Danger lurks outside the bunker, waiting for a moment of vengeance.