1Conversation Killers It's exciting, addictive and a little bit disturbing. It's a website where every click of the mouse lands you in a face-to-face conversation with a random stranger. But like its Russian namesake, Chat Roulette also has a very dark side. As 20/20's Pete Cronshaw discovers in his groundbreaking investigation, while you might think you're controlling the game, it's easy to be lured onto dangerous ground. You'll hear from Rebecca and her daughter Olivia, who have been scarred for life after their harmless peeping led them to a crime scene. And there's a warning for all of us from New Zealand's internet police - sometimes a harmless conversation really can prove deadly.

2Twisted Life She was a bubbly 25-year-old cheerleader, active and healthy. But then she decided to get the flu shot - and almost overnight went from a picture of health and happiness to a twisted vision of pain and stuttering. She's become the poster child of the anti-vaccine movement - and after footage of her jerky movements turned up on YouTube - a global internet joke. But as she tells 20/20, her bizarre symptoms, which include a strange foreign accent, are all too real - and we're there as she tries a desperate last measure to get better.

3Last Breath Coming soon to a car near you - devices that are supposed to stop drunk drivers in their tracks! They're called interlockers - and need a clean breath with no alcohol before your engine will start. But what if a stranger asked you to breathe into the gadget for them? In 20/20's latest social experiment, our hidden cameras are rolling as our actors stumble on the scene - you may be surprised who's willing to break the law.

4Wonder Drug We've spent decades giving kids the message to just say no to drugs, but on 20/20 you'll meet the parents who say they're proud that they've made the decision to give their children marijuana. Twelve-year-old Ryan has spent years battling OCD, and his mother Judy says after serious bouts of depression she made the tough call that medical marijuana rather than anti-psychotic medications was the only way to go.

5Buried Treasure They're everywhere - and we all want them. But when designer shoes cost thousands of dollars, how can bargain hunters really snag a good buy? We've all heard tales of fabulous spikes turning out to be fabulous fakes, and this week 20/20 delves into the treasure trove of sites offering huge discounts to give you the good oil.