The September queen - Gillian Bagwell

Jane Lane is of marrying age, but she longs for adventure. She has
pushed every potential suitor away-even those who could provide
everything for her. Then one day, adventure makes its way to her
doorstep, and with it comes mortal danger...

Royalists fighting to restore the crown to King Charles II implore
Jane to help. Jane must transport him to safety, disguised as a
manservant. As she places herself in harm's way, she finds herself
falling in love with the gallant young Charles. And despite his
reputation as a breaker of hearts, Jane finds herself surrendering to a
passion that will change her life forever.