A prospective client walks into your office and tells you the following story in a bad German accent. He works for a West African mining minister who makes the salary of a teacher, but has amassed a fortune by collecting “facilitation payments” from mostly Canadian multinationals in return for access to his nation’s mineral wealth.

Mr. Kayser, as he calls himself, asks you to discreetly stash up to $330 million in U.S. assets. He assures you that no laws were broken. But he uses the terms “illicit money” and “black money,” and says that buying a brownstone, jet and yacht in the minister’s own name would be “very, very embarrassing,” because the minister sometimes gives speeches against corruption under pressure from civil society. (You don’t know it, but in meeting another lawyer, Mr. Kayser admits: “So, OK, bribe. Is actually bribe.”)