Mia Julia Montes struggles to adjust to a new life in Baguio with her mother Teresa Ina Raymundo, her stepfather John Edu Manzano, and her half-brother Sam, while nursing a lingering resentment over the death of her biological father Rene. Despite John's misgivings, Mia secretly brings home a guitar from an abandoned house. Shortly afterwards, she attends a party at the Diplomat Hotel and meets Gio Gerald Anderson, a mysterious young man consistently dressed in the same outfit. Mia and Gio fall in love, with Gio teaching her how to play the guitar in a park with a young girl named Pauline, and Mia wakes up with roses all over her bed. Gio helps Mia overcome her trauma from witnessing her father's death and defends her from a group of bullies led by Wilmer. Yet Gio strongly resists having his picture uploaded by Mia on social media.
When Wilmer dies in bizarre circumstances following his encounter with Gio, Mia's family and friends question her involvement, noting that Wilmer committed suicide using Mia's cutter. When Mia explains that she was with Gio the entire time, she is told that she never seen with another person the entire time she was with Gio and was seen talking to herself, with all other evidence of their relationship deemed illusory. A desperate Mia convinces her group to accompany her to the park where she meets Gio, only to stumble upon a cemetery containing Pauline's grave. As Mia's sanity is questioned, she reconciles with Teresa when she clarifies the circumstances that led to her separation from Rene.
Mia later encounters Gio and chastises him for being untruthful to her. Gio then dares her to meet his family. That night, Mia arrives at Gio's house to meet with his family, only to be met coolly by them. Gio and his family reveal themselves as ghosts, prompting Mia to flee in terror. The next day, Mia confronts Gio at the cemetery for haunting her, but Gio demands that she join him in the afterlife and threatens to kill those closest to her, starting with her best friend Alvin JC de Vera. Mia and Alvin then meet Quinn, a nun who was Gio's previous girlfriend, who tells them that Gio had a turbulent family background that led him to commit suicide, and that Quinn's failure to join him in a suicide pact is what pushes Gio to haunt the living.
As Mia and Alvin try to protect her family from Gio's wrath, John tries to destroy the guitar, which turns out to have belonged to Gio, but has his hand burned by an angry Gio, who manifests himself as a poltergeist. When Gio threatens Sam, Mia reluctantly agrees to join Gio into the afterlife and goes with him to the Diplomat Hotel. Fr. Abellera, Mia's spiritual advisor, deduces that the only way for the hauntings to be stopped is for Gio's ashes to be blessed and goes to Gio's house with Sam. Meanwhile, Alvin follows Mia to the Diplomat Hotel while Mia reasons with Gio. Alvin tries to exorcise Gio, but the latter partially possesses Alvin and leads him to self-harm while Fr. Abellera and Sam are tormented by the ghosts of Gio's family. In tears, Mia agrees to die on condition that her loved ones will not be harmed, and jumps off a ledge. However, Sam manages to bless Gio's ashes in time, and Gio catches Mia before she falls further. Gio tells Mia he loves her before they share one final kiss as he departs to the afterlife, finally at peace.
Some time later, a garage sale is being held for Gio's old things. A woman picks up Gio's guitar and starts to play it, only for a string to break and blood to appear on her face.
