A snakehead has teeth like a shark, a taste for blood and even walks on land. It is an insatiable alien predator that can obliterate the food chain and overpower native life. It mysteriously showed up near a small Maryland town and now can be found coast to coast. Scientists are sounding the alarm. It is a showdown of man vs. fish as scientists and anglers work together in the fight to defy it, control it - and stop it from destroying everything in its path.