Paris, 1910. The streets of the city are flooded. The Eiffel Tower looms over a temporary lake and certain streets sport makeshift bridges so Parisians can go about their daily routines. But spirits are high for the citizens of this romantic city, including those of Emile (Jay Harrington), a lovelorn cinema projectionist, and his madcap friend Raoul (Adam Goldberg), a delivery man by day and inventor by night.
Raoul is equal parts brazen attitude, affectionate demeanor (mostly towards Catherine, his trusty truck) and limitless energy. His unbridled enthusiasm for discovery and breaking the rules lands him and Emile in the perfect setting for unintentional mischief: an eccentric scientist s greenhouse. Explosions follow. Once the clouds of smoke clear, Raoul and Emile realize that a monster has been let loose onto the soggy streets of Paris.
Feeling some responsibility but mostly filled with a sense of adventure, the friends plunge headlong into a chaotic monster hunt. Only after the intervention of Raoul s former classmate Lucille (Vanessa Paradis), now a celebrated cabaret singer, do they consider the possibility that the terrifying monster may not be as menacing as he appears. But can the group save the beast from the corrupt police chief (Danny Huston), an ambitious mayoral candidate who needs to prove he s doing something to keep the waterlogged streets of Paris safe?
Throughout their adventures, the ragtag gang of monster hunters encounters many colourful characters, including a sweet cinema ticket agent, a saucy nightclub owner and an irritable monkey who may be the best communicator of them all.