Finished Challenge 1 and looking for something to read while waiting for Challenge 2 on Thursday? Why not take a look at the following artilce in Nautil.us:
https://nautil.us/issue/6/secret-codes/the-artist-of-the-unbreakable-code
It's all about Elgar (which gives me an idea for a future story come to think of it) and the enigmatic Dorabella cipher. Lots of people have tried to make sense of it, and maybe one of you will succeed.
Harry