His Best Friend

What happens when an international superstars sister is off to college and lives at her brothers flat the whole time? Especially when one of his best friends seems too awfully familiar. Not 'Hi-Lets-Be-Friends-And-Eat-Cupcakes-Together!' familiar but 'Hi-Lock-Your-Door-Because-I'll-Act-Nice-To-You-But-I-Will-Kill-You-Slowly-In-Your-Sleep' kind of familiar. (I still suck at descriptions)