Meet Chris Heifner, overachieving drug runner for a Mexican marijuana cartel. But he wasn’t always. This one-time econ student from Texas—broke, deep in debt, and facing eviction with a growing family to support—yielded to the temptation that he had resisted countless times before and went to work for his best friend from college, Jake Andes. But it wasn’t exactly a Career Day kind of job. Andes was a big-time dealer, captaining a $25-million-a-year empire. Heifner became a mule, running m...