Fin Ian Ziering and his wife April Wexler Tara Reid travel to London with their young son Gil Shepard Billy Barratt to attend a NATO briefing about the escalating sharknado threat. Meanwhile, Nova Clarke Cassie Scerbo and her team investigate a temple hidden beneath Stonehenge, where Nova summons Fin to help her. They uncover a shrine to an ancient shark god and claim an artifact, which unintentionally unleashes a new kind of sharknado that contains a dimensional vortex inside it. The storm tunnels toward London, forcing Fin to rally the Buckingham Palace guards in a desperate bid to stop it. Though they endure the onslaught, Gil is dragged into the cyclone and vanished from sight.
As the danger unfolds, Fin, April, and Nova realize Gil is still alive and begin tracking him through a signal emitted by a helmet that he received earlier from British scientists. Their pursuit leads them aboard an airship built and piloted by Dr. Angel Geraldo Rivera, but the craft is caught in another sharknado and crashes. Fin, April, and Nova steal skis and continue the chase as the storm drives them down snowy slopes, ultimately plunging them into yet another sharknado that transports them to Sydney. There, April’s cybernetic body is badly damaged in a shark attack, and Nova introduces Fin to the Sharknado Sisterhood, a global alliance dedicated to destroying sharknados. Nova’s allies Orion Olivia Newton-John and Electra Chloe Lattanzi are part of the group, as is Fin’s cousin Gemini Masiela Lusha, who oversees the ship carrying nuclear waste from Niagara Falls. Fin is furious that Gemini’s role in the Sisterhood was kept secret and sets off with the upgraded April to locate Gil. A sharknado strikes Gemini’s ship, absorbing the nuclear waste and mutating into a massive, shark-filled entity that heads for Japan.
In Rio de Janeiro, Fin and April meet another Sisterhood member at an old church and learn more about the ancient myths surrounding sharknados and the vortex, including the notion that “the Earth has many portals.” An art thief steals the artifact during their discussion, sparking a high-speed chase that ends in Rome’s Colosseum when a sharknado teleports their vehicles. The pair recover the artifact and are summoned by the Pope Fabio, who urges Fin to press on in his mission to save Gil and the world, even gifting him with a mystical chainsaw for the battles ahead. With the artifact, Fin and April summon a sharknado and almost reach Gil, but he slips away and all three are pulled back into the vortex.
The duo lands in Tokyo just as a colossal mass of sharks—now dubbed “Sharkzilla” by the world media—rips through the city. Gil is trapped inside the creature, and Nova arrives with the remaining Sisterhood members to confront the threat. Nova skydives into Sharkzilla and clawed her way toward Gil, but military jets bombard the mass and trigger a cataclysmic explosion. Gil vanishes in the blast, while Nova is mortally wounded and dies after Fin forgives her and accepts her as part of their family. A short time later, Fin phones his son Matt, who tearfully tells him that all their family members are dead—before Matt is killed by a sharknado striking the family farm in Kansas. Grief-stricken, Fin and April decide to return the artifact to Stonehenge, hoping to halt the global outbreak.
Their plan backfires when the sharknado they summon instead plucks them from Earth and drops them at the Pyramids of Giza in Egypt. There, hieroglyphs reveal that the shark god and the vortex are tied to the Earth’s core. The pair discovers an ancient mechanism that opens the pyramids to absorb the vortex energy, seemingly ending the crisis—until the device reverses, and the vortex energy erupts from the planet, triggering a planetary sharknado. Gemini is killed in Tokyo as the world reels. With no clear way to shut down the mechanism, Fin and April rush outside as a colossal sharknado and a towering tsunami bear down on them. Using a staff found in the pyramid to hold back the storm, April absorbs the entire planetary vortex with her energy-absorbing abilities, sacrificing herself to end the catastrophe. Her body explodes, leaving Fin seemingly alone on a devastated Earth.
He clings to the hope of survival by gathering April’s head in a bag attached to the staff, wandering the ruined world in search of any survivors. Then, a truck appears in a beam of light, driven by a dramatically aged Gil Dolph Lundgren who, after Sharkzilla’s explosion, has spent the intervening years developing a way to use the sharknado as a time machine. Reunited, Fin and Gil set off into the past to stop the sharknados once and for all and save their family and friends.
