Ben Fogle travels to Botswana to join a pilot research study which aims to do the unthinkable - swim with Nile crocodiles. These ancient reptiles spend roughly 80% of their lives underwater, yet relatively little is known about their subaquatic lives. Now for the first time, crocs have become the biggest killers of humans in Africa - up to 700 this year - so new research is vital. Wildlife experts Brad Bestelink and Andy Crawford have devised a method of diving with crocodiles which they believe to be safe. For the first time, leading crocodile authority Adam Britton has come to test their theories, and see if they can reveal new information about these magnificent beasts. But after the team's underwater cameraman Mike Pitts has a near miss with a crocodile, will they continue with the task they have set themselves?