In my new book, James’s London residence, a townhome, is in Cavendish Square. Susan, who still lives with her parents, the Duke and Duchess of Bradford, have their London home in Grosvenor Square. James and Susan meet secretly in Green Park. 
The funny thing is that I made it all up even though I’d heard of these places before but until I looked up a map of 1815 London I didn’t know if they were close to each other.
They are!!!