Tonight, we're in Florida, where families with children crowd the beaches and theme parks, and men who prey on children crowd the Internet.

Over the course of our four day investigation, 21 men showed up at Dateline's house on the beach -- and "fun in the sun" is not what was on their minds.

Chris Hansen with an all-new Dateline investigation: "To Catch a Predator."

Here's a preview from Chris on the 'Inside Dateline' blog:

"Many of the men ultimately admit their intentions and sometimes go into great detail about their online addictions and compulsions that led them to our door. But every once in a while, I run into someone who comes up with what he thinks is a plausible story-- an 'innocent excuse' if you will -- for being in the wrong place at the wrong time. Such is the case with the first man you’ll meet tonight. He’s a 32-year-old successful real estate executive who was chatting online with a decoy posing as a 13-year-old girl. As you’ll see, he’s a pretty confident guy when he walks into our house. When I start to ask him questions, he says he was in our area checking on some property he owned and had pulled off the road near our house to get a good view of the space shuttle blasting off." Click here to read more.

That's tonight at 8 p.m./ 7 central on Dateline NBC.