What happens in London - Julia Quinn

When Olivia Bevelstoke is told that her new neighbour may have killed his fiancée, she doesn't believe it for a second - but still, how can she help spying on him, just to be sure?

So she stakes out a spot near her bedroom window, cleverly concealed by curtains, watches and waits... and discovers a most intriguing man who is definitely up to something.

Sir Harry Valentine works for the boring branch of the War Office, translating documents vital to national security. He's not a spy, but he's had all the training, and when a gorgeous blonde decides to watch him from her window he is instantly suspicious. But just as he decides that she's nothing more than a nosy debutante, he discovers that she might be engaged to a foreign prince, who could be plotting against England. And when Harry is roped into spying on Olivia, he realises that he may well be falling for her himself...