A Love For All Time by Laura Landon

A built-in family is not what Lady Cassandra Worth intended to take on, especially after having sworn never to marry again. But that is what the reckless, destitute special agent for the crown Colonel Quinten Beckham offers.
When he inherited the title Earl of Rosemont, he was left not only a rundown estate and a mountain of debts, but his brother’s two young children. Now he must find a way to raise his two nieces, keep his estate afloat, and continue his dangerous undercover work.
The only way he can see to manage it is for Lady Cassandra to accept his proposal. But can he keep her from falling in love with him, so her heart doesn’t break when he leaves her a widow?