Married by Morning by Lisa Kleypas

For two years, Catherine Marks has been a paid companion to the Hathaway sisters—a pleasant position, with one caveat. Her charges’ older brother, Leo Hathaway, is thoroughly exasperating. Cat can hardly believe that their constant arguing could mask a mutual attraction. But when one quarrel ends in a sudden kiss, Cat is shocked at her powerful response—and even more so when Leo proposes a dangerous liaison. Leo must marry and produce an heir within a year to save his family home. Catherine’s respectable demeanour hides a secret that would utterly destroy… Read more.