My best friend, the scammer

Someone by the name of Charles phones to remind me that he is my very best friend. Charles who? Well, when someone calls and addresses you by your first name, claiming that he and I are the closest of comrades and you have no clue what he is talking about, you are allowed a few questions.

Charles said we spoke last December and that I failed to take up his offer of shares in a company quoted on the second market in Frankfurt, where stocks are so lightly regulated that it makes the United States' Pink Sheets look blue chip by contrast.