Andrew Yancy-late of the Miami Police and soon-to-be-late of the Monroe County sheriff's office-has a human arm in his freezer. There's a logical (Hiaasenian) explanation for that, but not for how and why it parted from its shadowy owner. Yancy thinks the boating-accident/shark-luncheon explanation is full of holes, and if he can prove murder, the sheriff might rescue him from his grisly Health Inspector gig (it's not called the roach patrol for nothing). But first-this being