It stars Bérénice Bejo as a grieving marine biologist who is forced to face her tragic past in order to save Paris from a bloodbath when a giant shark appears in the Seine.

[3][4] Near the Great Pacific Garbage Patch, marine researcher Sophia Assalas and her team search for Lilith, a tagged shortfin mako shark.

Environmentalists Mika and Ben inform Sophia that Lilith's tracking beacon is still active and that she has travelled from the Pacific and up the River Seine and is seemingly trapped in the city.

The mayor refuses, emphasizing the event's importance for focusing global attention on Paris during the run-up to the Olympic Games which billions of euros have already been spent on.

Mika does not heed to their warnings to get out of the water, and after she pets the juvenile shark, Lilith attacks and kills her, causing a mass panic that leads to many injuries and twelve deaths, including Ben and Leopold, a police officer on Adil's team.

In the aftermath Sophia and Adil find the juvenile shark dead, and after examining it they discover that it's a female that mutated to adapt to fresh water and became pregnant through parthenogenesis, like Lilith.

As the mayor declares the triathlon open, and swimmers take to the water, Adil's team Caro, Adama, Angèle and Markus begin to execute the plan.

The website's consensus reads: "Marrying environmental themes with bloody thrills, this Gallic entry into the shark attack canon ultimately lands on the right side of ridiculous fun.