I don't know if you remember me from your time at Hogwarts, but I was a student of yours the year you taught DADA. Roger Davies, 5th Year Ravenclaw. I started as Captain of the Quidditch team that year.
I was told by a mutual acquaintance of ours that I should speak to you about membership to a private sort of club that the two you are apart of. A recent encounter with a snake prompted me to send this owl.