This is a slightly different take on the friend-to-lovers trope -- Bianca is Caleb's sister, Greta's BFF. While Greta's brother was deployed, Greta asks Bianca to write a letter to him. Bianca doesn't even think she'll receive a response from Caleb, much less that she and Caleb would become pen pals for five years while he's away.
The book is told mostly through Bianca's POV so we find out early on that Bianca has been pining over Caleb since she was very young, even before she started sharing letters with Caleb. Bianca doesn't yet know that Caleb, through their letters, fell in love with her during those five years. Instead of talking to Bianca when he gets home, Caleb pushes her right into his bed, then he's proposing marriage the very next day.
Bianca is completely overwhelmed by this obviously, so Caleb needs to slow his roll and explain his feelings to Bianca and romance her rather than just give her orders.
I have to say that my biggest issue with this book is that it rests on a common theme in romance novels with a BBW. Bianca is insecure and has no idea that she's a beautiful woman that men want; not just Caleb but others too. There's a light love triangle here with a colleague of Bianca's who wants to date her, but it's rather weak considering we know Bianca is in love with Caleb and Caleb isn't letting another man get his hands on Bianca without a fight. The problem is that Bianca just doesn't believe she deserves anyone's ardor because she's not a single digit size. Only size 6s can believe they are worthy of love and affection from a handsome man??? Please spare me!!
That's just a personal pet-peeve of mine that so many authors write female characters this way. Anyway, that's a rant for another day and another book! Overall, this novella was cute and sexy.