A Euro-based English reading list for 13 year olds?
Take a look at Madeleine L'Engle. Her "A Wrinkle in Time" is very good. Most of her other books are also good.
http://en.wikipedia.org/wiki/A_Wrinkle_in_Time"The Scarlet Pimpernel" is another good book in the same milieu as Hugo's books.
http://en.wikipedia.org/wiki/The_Scarlet_PimpernelI really liked Josephine Tey's "A Daughter of Time."
http://en.wikipedia.org/wiki/The_Daughter_of_TimeAnd this might be also good to finish the summer with. You might be able to find it running in a local stock production.
http://en.wikipedia.org/wiki/A_Man_for_All_Seasons