Brighter than the sun - Julia Quinn

Eleanor Lyndon was minding her own business when a lord of the realm fell - quite literally - into her life. When Charles Wycombe, the dashing and incorrigible Earl of Billington, toppled out of a tree and landed at Ellie's feet, neither suspected that such an inauspicious meeting would lead to marriage. But Charles must find a bride before his thirtieth birthday or he'll lose his fortune. And Ellie needs a husband or her father's odious fiance will choose one for her. And so they agree to wed.

Ellie never dreamed she'd marry a stranger, especially one with such a devastating combination of rakish charm and debonair wit. She tries to keep him at arm's length, at least until she discovers the man beneath the handsome surface. But Charles can be quite persuasive - even tender - when he puts his mind to it, and Ellie finds herself slipping under his seductive spell. And as one kiss leads to another, this unlikely pair discovers that their marriage is not so inconvenient after all...and just might lead to love.