Grace Livingston Hill 
The Strange Proposal [EPUB ebook] 

Mary Elizabeth Wainwright, carefree daughter of a famous family, had expected to have fun at her cousin’s wedding. What she hadn’t expected, however, was to end up being the maid of honor—or to have John Saxon, the handsome best man she met just before the ceremony, proclaim his love for her during the wedding recessional!
Now many forces threaten to pull Mary Elizabeth and John apart: distance, social standing, finances, a lost lava letter, belief in God, and a wealthy man who is determined that nothing—and no one—will stop him from claiming Mary Elizabeth as his own…