Boston is now home to the nation's highest rate of opiate (heroin, oxycodone) addiction and overdose. Vanguard correspondent Mariana van Zeller investigates the story behind the dramatic spike in drug abuse over the course of the last decade and along the way uncovers a disturbing new trend: an alarming escalation among addicts from prescription drugs to heroin, a cheaper and more potent alternative to OxyContin that's all too readily available on the streets of New England.