An elite handful of fish are capable of living and thriving in both fresh and saltwater. Among these specialists are aggressive man-eaters, venomous giants and a wickedly armed beast that hails from a bygone age. In this special edition of River Monsters, biologist and extreme angler Jeremy Wade relives his thrilling encounters with some of these fearsome intruders that swim in from beyond the surf. Jeremy reveals how our understanding of these predators has shifted dramatically in recent years and answers pertinent questions about what draws these ocean-dwelling hunters into freshwater in the first place and how they are capable of crossing what is normally an impenetrable barrier.