>> what's on the agenda for tonight? >> hidden cameras are rolling, the suspect's running and police are ready. >> get down! get down on the ground. >> we arrested a very significant number of pedophiles. >> it's a new investigation. chris hansen with "to catch a predator." >> you'd think they'd know by now. suspected predators on the web, then at the door. thanks for joining us. i'm stone phillips. >> i'm ann curry. this time we're in long beach, california, where the long arm of the law has reached out and grabbed more than three dozen men in just three days. >> chris hansen has the latest. again, we want to warn you, some of what you will see and hear is explicit. >> hey, come on in. this way. how are you doing? >> looks like you fell asleep. >> kind of. how was your drive? >> long. >> 22-year-old cory blagg is walking into "dateline's" undercover house in long beach, california. a house with 15 hidden cameras. they're recording every move he makes.