Split Second (King & Maxwell #1)

Michelle Maxwell has just wrecked her promising career at the Secret Service. Against her instincts, she let a presidential candidate out of her sight for the briefest moment and the man whose safety was her responsibility vanished into thin air. Sean King knows how the younger agent feels. Eight years earlier, the hard-charging Secret Service agent allowed his attention to be diverted for a split second. And the candidate he was protecting was gunned down before his eyes. Now Michelle and Sean are about to see their destinies converge.