The animal kingdom possesses a fearsome arsenal - a variety of extreme weapons used in epic battles to gore, stab, crush and batter. But are they more than just instruments of deadly force? For Professor Doug Emlen, it has been his lifetime's ambition to discover the secrets of nature's arms races, what triggers them and what they can teach us about the most formidable weapons on earth - our own.

Otters are playful, adaptable and champion swimmers - they've captivated cameraman Charlie Hamilton James for the last 25 years. He's filmed them more than anyone else and now, through the eyes of three orphaned river otters, a set of ground breaking experiments and some incredible wild encounters, Charlie wants to reveal their survival secrets and exactly why he believes they're so special.