Spy Secret Messages

I love Usborne books for children, and so does Wolfie, so I end up buying lots of them. And they have a handful of books of espionage games and activities. There is one we particularly like, especially when we travel, it's called Spy Secret Messages. It's a small pocket book, smaller than a pocket book actually, and it's all about deciphering spy codes and finding the meaning of messages. It's really great fun. The only drawback is that soon we will have finished every activity in the book. I guess I will need to find more gamebooks in the genre, from Usborne and others.