In its second hour, "It's a Sin" becomes dazzling. One way to understand Davies's work is through the lens of dramatic irony. This term refers to any moment when we know things the characters do not know. ("Mad Men" was also a major factory for dramatic irony.) So--for example--we see one character rejecting another's blow-job offer when London enters the picture. ("You're from London? That's dangerous...." As if HIV would not have traveled to smaller towns.) The scene becomes odder still when the London boy makes a bold claim: "HIV is only in New York. People from London are fine." In another corner of Davies's world, a young woman struggles to help a friend with HIV. Should she shatter the mug this friend was drinking from? Should she wrap the mug's shards in a towel -- and bury the towel? Should she always be wearing rubber gloves? You feel the sense of panic when the friend's sister visits: She cannot begin t...