As chaos envelops Los Angeles, Brad (Rory Cochrane), an unemployed musician, is left isolated in his home while his wife Lexi (Mary McCormack) is out working. An emergency broadcast reveals the city is under siege from the deadly fallout of suspected dirty bomb explosions, leading to a rapid spread of toxic fumes. In a frantic attempt to reach Lexi, Brad faces the frustration of a busy signal on her phone. When he decides to venture out, he finds himself thwarted by police barricades, forcing him to remain trapped indoors.
Meanwhile, a mysterious intruder, Alvaro (Tony Perez), takes refuge in Brad’s home. He recounts how he was displaced from his neighbor's abode, which now offers no protection against the encroaching poison outside. The radio reports that survivors are being quarantined, and to stay safe, families are advised to seal their homes against the spreading toxins. In light of this, Brad and Alvaro begin to fortify their environment with makeshift barriers of duct tape and plastic sheeting.
As time passes without any sign of Lexi, Brad becomes increasingly distraught, fearing for her safety. He places some of her belongings – clothing, snacks, and water – at the back door, hoping she will return soon. When she finally appears, dust-laden and frantic, Brad hesitates to let her in, leading to a heated exchange. Lexi, in her desperation, breaks her phone against the window, which shatters in frustration. With Alvaro’s help, Brad quickly blocks the breach while trying to ease Lexi’s rising panic.
In the main bedroom, Lexi receives a harrowing phone call from her mother, who is acutely aware of the dire situation and may even be infected. Dismissing the gravity of their circumstances, Lexi clings to the belief that things will be alright. Just then, Alvaro unexpectedly announces his intention to seek out his wife, ignoring Brad’s pleas for him to stay. With his decision made, he disappears into the toxic fallout as rain begins to fall around them.
Night descends, bringing with it unsettling noises from within their refuge. Lexi's instincts kick in as she alerts Brad to a possible threat. A masked stranger, Rick (Jon Huertas), emerges from the darkness, claiming that a ship is anchored offshore, ready to assist those afflicted with the mysterious illness. With no time to lose, Lexi and Rick resolve to gather more information, while Brad remains at the house, glued to the radio updates detailing the grave situation. The reports increasingly warn of a hybrid virus that preys on the respiratory system, leaving its victims gasping for breath.
As evening progresses, Brad is visited by Corporal Marshall (Max Kasch) and his team, who question him with suspicion regarding their home's defenses, potential visitors, and contact with the outside world. Brad expresses his worries about Lexi and her recent outburst that resulted in her phone breaking. The corporal insists on collecting a dust sample from the shattered device, before warning that Lexi must not be permitted back inside.
The following day, Lexi arrives alone, noticing a red tag on their door, which signals danger. In search of comfort, she calls her brother Jason (Will McCormack), wanting to connect despite the turmoil enveloping their lives. As they converse, it seems they may find peace. However, chaos interrupts as soldiers appear at their doorstep, taking Lexi away and preventing Brad from reaching her. One soldier offers a glimmer of hope, informing Brad that the virus cannot thrive in well-ventilated spaces, explaining why deaths have been relatively low.
Yet, as fate would have it, Lexi’s inadvertent introduction of the virus through the shattered window has turned their home into a breeding ground for its spread. Brad’s efforts to secure the house expose him to the very danger he sought to evade. With soldiers preparing to spray potent chemicals to cleanse the area, Lexi can only scream in anguish at the thought of Brad being trapped inside. The soldiers proceed with their harsh reality, squandering any shred of hope for Brad's survival.
In a heart-wrenching finale, we see Lexi, emotionally shattered, being cared for by a kind nurse in an ambulance. As she grapples with the enormity of her loss, the painful irony resonates in her life – her cell phone’s persistent ringing serves as a cruel reminder of what has been taken from her.
