Given the question: Build a movie plot around this: What are Souls? Extraterrestrial parasites who've taken over the human race
The answer is:
In 2000, an American military pathologist is commanding a reluctant Korean assistant to violate protocol by dumping over 200 bottles of formaldehyde down the drain, leading into the Han River. Over the next few years, there are sightings of a strange amphibious creature in the water ways.Six years later, in Seoul, Park Gang-du (Song Kang-ho) is a seemingly slow-witted man who runs a small snack-bar with his father, Hee-bong (Byeon Hee-bong). Also with him is his brother and sister; national medalist archer, Nam-joo (Bae Doona), and alcoholic former-activist Nam-il (Park Hae-il), as well as his daughter, Hyun-seo (Go Ah-sung).While Gang-du is delivering food to some customers, he sees a crowd along the Han River. They witness a huge creature hanging from the Wonhyo Bridge, which then jumps into the water. At first, it seems as though the creature has swam away, encouraging the public to bait it back with food. Moments later, the creature rises out of the river and runs amok. After the creature causes chaos and kills a number of people, Gang-du and an American man attempt to kill the creature with a metal pole, but in the process the American is seriously injured and they only succeed to anger it and starts pursuing Gang-du. Gang-du grabs a girl's hand which he believes to be Hyun-seo and starts to flee. When he realizes he isn't holding Hyun-seo, he turns to see the creature running towards her. The creature then snatches Hyun-seo and dives back into the river.During a mass funeral for the victims of the creature (including Hyun-seo, believed dead by her family) Government representatives arrive and forcefully quarantine all those who have been in direct contact with the creature, including Gang-du and his family. The South Korean government announces that the creature is not only a direct danger, but also the host of a deadly, unknown virus (which is the formaldehyde from the drain) as the American (who lost an arm to the creature) is discovered to be infected with it.While in quarantine inside a hospital,...