In 2005, NASA uncovers a distant planet known as Planet-G, which shares Earth-like qualities, and sends out a powerful signal from a communication array nestled in Hawaii. Meanwhile, slacker Alex Hopper finds himself in hot water after being arrested while trying to impress Samantha Shane, the daughter of Admiral Terrance Shane, who commands the U.S. Pacific Fleet. Frustrated by Alex's aimlessness, his older brother Stone Hopper, who serves as a Commander under Terrance, insists that Alex join the United States Navy.
Fast forward to 2012, and Alex now holds the rank of lieutenant aboard the USS John Paul Jones, with Stone commanding the USS Sampson. Despite being in a relationship with Samantha, Alex's repeated disciplinary issues threaten his career. On the verge of proposing to her, tension mounts when he engages in a fight with a Japanese naval officer, who had previously bested him in a soccer match. Their naval fleet embarks on RIMPAC exercises in Hawaii, where misfortune follows as five alien vessels appear in response to NASA's signal. Chaos ensues when these crafts crash into Earth after colliding with an orbiting satellite and near the Hawaiian waters.
As the John Paul Jones, Sampson, and Japan's Myoko investigate the mysterious vessels, they become ensnared in a force field erected by the alien mothership, which isolates them from the rest of the fleet commanded by Admiral Shane. In a fierce exchange, the aliens swiftly destroy the Sampson and Myoko, severely damaging the John Paul Jones, which claims the lives of its commanding officers. With limited options, Alex rises to leadership as the senior officer left, grieving the loss of his brother, Stone.
Meanwhile, Samantha, a physiotherapist, is out assisting retired Army veteran Mick Canales on a hike when they encounter scientist Cal Zapata, who warns them about the aliens' plans to send signals home via NASA's satellite. With time ticking away, they work together to secure a means of communication to warn the John Paul Jones.
As the crew of the John Paul Jones grapples with their new reality, they capture an alien, opportunity for strategy arises—Alex gains insight into an impending invasion. After determining the aliens are sensitive to sunlight, Alex collaborates with Captain Nagata to engage the alien fleet creatively, reminiscent of a strategic board game. Their efforts lead to the destruction of two alien ships; however, they must face the formidable mothership and the tower sustaining the force field.
Compelled to thwart the alien threat, Alex and the remaining survivors procure the decommissioned USS Missouri, reactivating the battleship with the help of veterans. Expertly dodging alien fire, they retaliate with the Missouri's powerful main guns, finally breaking the alien's force field. In a climactic final act, Alex sacrifices the last shell to obliterate the communications array, rendering them momentarily defenseless. Luckily, this opens the door for allied fighter jets to swoop in and eliminate the remaining alien threat.
The story concludes with a ceremonial tribute to the navy personnel, where Alex gathers the courage to ask Admiral Shane for Samantha's hand in marriage. Despite initial resistance, the Admiral agrees to a discussion over lunch. In a thrilling post-credits scene set in Scotland, suspense builds as children run off in fear from an ominous alien hand emerging from a broken object, hinting that the adventure may not be over just yet.
