Countryfile is in Hertfordshire, where Charlotte Smith meets the man who's made it his sole mission to save the barbel in the Old River Lea. Sean Fletcher builds a home fit for a Kingfisher and forages for a wild dinner. John Craven returns to his days as a scout and cooks up a storm on a woodland fire. And Adam Henson discovers the estate where rewilding and farming sit side-by-side. Now in its fifth year, what effect is culling badgers actually having on rates of TB in our cattle? Tom Heap's looking at the science behind this controversial practice.