I've finished! I really liked this book. I have now read the Wikipedia summaries of both Colm Tóibín and Henry James to have a better biographical understanding of both men as well as the key themes of their works. I found this New York Times book review extremely insightful into what motivated Tóibín to write about James and what influenced him in the manner he chose to portray James. The reviewer also identifies other sources about James and whether some of the events that Tóibín fictionalized are realistic or embellished from the viewpoint of these other sources.
http://www.nytimes.com/2004/06/20/bo...l?pagewanted=1
I was fascinated by imagining Lamb House and the garden. Here's an article on its history.
http://www.ryemuseum.co.uk/lamb-house/
Lastly I wanted to mention that the Wikipedia article on the Protestant Cemetery in Rome is extremely interesting. What a long list of famous authors and artists buried there! It includes a photo of Story's sculpture, Angel of Grief, which is very beautiful and moving.