Project Duke by Mariah Stone

Overprotective rake. Daring bluestocking. A marriage of convenience between opposites…who fall head over heels.

Marriage? “No thank you, sir!” has always been Lady Calliope Seaton’s answer. But she needs access to naval documents to rescue her brother Spencer. And she’ll do anything to get them—even wed disreputable navy officer Nathaniel Fitzgerald, the Duke of Kelford.
Nathaniel has been obsessed with the daring bluestocking since she broke into his office. And to claim his inheritance, he needs a wife and an heir. So he proposes a marriage of convenience.
Moving into Nathaniel’s decaying Mayfair mansion and taking on his three untutored sisters would challenge even the bravest new bride. But it’s not long before Calliope is fixing up his home, winning over his sisters and claiming his heart.
Falling hard for his adventurous wife ignites Nathaniel’s fierce protective instincts. Especially when he learns there may be a baby on the way—and a threatening stranger sends knife-wielding attackers.
Calliope will never allow herself to be caged, and trying to keep her safe is turning Nathaniel into a tyrant he loathes. Will their differences destroy them, or can love win over fear?