Blackmail was a dirty business and Donald Lam liked to stay clear of it. But for his partner, Bertha Cool, no business was too dirty to handle at the right price. And the price for this job was certainly right.What was wrong, though, was a payoff for pictures that weren’t worth a dime, a free dinner that cost the blackmailer his life, and more than a couple of double-crosses that framed Donald Lam quite neatly for a charge of murder …