On July 1, 1916, amid the shadow of World War I, a quiet New Jersey shore is watched over by local lifeguard Alex Trednot [Colin Egglesfield] as crowds mill along the surf. His best friend Stanley [Mark Dexter] and his ex-girlfriend Alice [Jenna Harrison] stop by with a casual question about a wedding cake, a moment that will soon feel irrelevant in the face of a brutal threat. Suddenly, beachgoer Charles Vansant [Karl Thaning] is attacked by an unseen force, leaving him badly hurt and ultimately dead. Alex believes a shark is responsible, but because he didn’t witness it clearly, his warning is dismissed by officials and the beaches remain open. Cap [John Rhys-Davies], a seasoned boat captain who has hunted sharks, senses the danger too, even as Mayor Perillo [Patrick Lyster] tells him the city won’t close the beaches without confirmation from experts. The tension between public safety and wartime complacency threads through the town as the alarm begins to rise.
That evening, President Wilson’s visit to the Jersey Shore amid calls for safety only amplifies the pressure to keep things orderly. Alex’s boss, Commissioner Meel, offers a blunt reassurance that the attacks won’t recur, even as Alice asks him whether there are lingering regrets about her and Stan’s upcoming marriage. On July 7, the danger intensifies when another lifeguard, Danny Bruder, is pulled under while attempting to retrieve two swimmers who have drifted too far from shore, and he dies too. With another fatal blow, Alex resigns in frustration, convinced that something deadly stalks the sea and that money or politics should not obscure the truth.
Across the river in New York City, Michael Schleisser [Jamie Bartlett], a wild animal wrangler, reads about the attacks and travels to New Jersey to understand what is happening. At a press conference, Museum Director Dr. Frederick Lucas and ichthyologist Dr. John Nichols [Colin Stinton] examine the evidence and search for a way to prevent further tragedies. Stan tries to convince Alex to return to his post, but Alex remains wary of working under someone who might prioritize business over people. Cap offers Alex a job helping to install steel nets to deter future attacks, a plan that could reignite his faith in protection, even as a boat crewman on Cap’s vessel misjudges a sighting and fires on a diver.
With the steel nets in place, the beaches reopen and the mood lightens—until a young boy named Lester is attacked downstream. A mother’s screams ripple through the park as Cap races to warn people, but the threat proves elusive. Cap spots the shark moving upriver toward Matawan Creek and tries to warn the towns, but many dismiss him as a fool. The search intensifies; Stan and his friends dive in with the hope of finding Lester, yet the river refuses to yield him. For hours, the team fights against the river’s current, with one injury after another reminding them of the stakes. In a moment of tense relief, Stan finds Lester, but the relief is short-lived as the shark strikes again, knocking Lester from Stan’s arms. Alex lashes out with a paddle to free the boy, and Cap pursues the predator.
A picnic in a riverside grove becomes a new flashpoint as a mother and her daughters glimpse the threat and attempt to warn a group of swimming boys. Cap arrives in time to ram the shark away, forcing it to release the boy Joseph Dunn before it slips back toward the sea. Yet the danger lingers, and Stan’s condition worsens as they race him toward medical help.
On the train to the hospital, Stan dies from his injuries, a crushing blow that hardens the town’s resolve to end the terror. The townsfolk grow restless, and a wave of vengeful hunts sweeps the shore; Cap seems to have captured the creature, but Dr. Nichols urges a cautious, scientific approach. He suggests the shark may be a juvenile great white—perhaps a bull shark that has ventured far upriver—and that the team should not act alone but rather with a plan and support from experts.
Alex and Schleisser meet to discuss the shark’s true identity: this is not a monster to be killed for sport or money, but a creature with a purpose that must be understood. The trio—Alex, Cap, and Schleisser—join forces to hunt the right shark. Schleisser’s net is deployed beneath a small boat, and the juvenile great white finally surfaces, becoming entangled in the improvised trap. The struggle is long and exhausting, but the shark eventually dies of exhaustion after being towed ashore.
The team hangs the captured shark for display, and Dr. Nichols confirms its classification as a juvenile great white. Alex, now faced with a future that may lie in science as well as rescue, asks Nichols about becoming an ichthyologist, hinting at a new path. He and Alice reconcile, and their friendship deepens as the threat is finally laid to rest. An autopsy reveals that the creature had consumed about 15 pounds of human flesh and bone, underscoring the gravity of the encounters. In the end, four people were killed, one was severely injured, and Lester’s remains were recovered; scientists remain intrigued and unsettled by the shark’s unusual behavior and the mystery of why such a creature would threaten humans in these waters.
