A human woman named Asherina from an ancient underground civilization meets with military Commander Beaker, revealing that her people have lived secretly beneath the surface for 600 years and are genetically similar to surface humans. Despite Beaker's skepticism and Asherina's refusal to reveal her city's location or allow official documentation, she joins a classified military project and moves in with team member Ella's family, bringing her husband and baby as they prepare for some urgent, undisclosed threat.