The Husband Mission by Regina Scott

Katherine Collins is on a mission. With no means and few prospects, the spirited spinster is financially beholden to her stepsister Constance, who stands to inherit a large fortune–if she marries in the next six weeks. What better than to present Constance with the perfect husband, Alexander Wescott, Lord Borin? After all, Katherine has been spying on the handsome, wealthy viscount, just to make sure he’s the man she hopes.

Alex cannot understand why he’s under surveillance, but it seems to have something to do with the intriguing Katherine. Rejected for service by England’s spymaster and encouraged to set up his nursery instead, he ought to be searching for a wife. But what wife can compare to the excitement of international espionage? Unless, of course, she’s up for a little espionage herself.