In Friendship, Maine following the death of her father, neurotic and spoiled heiress Carrigan Crittenden discovers she has only been left Whipstaff Manor in his will while his vast wealth has gone to several charities. Carrigan and her lawyer Dibs find a map within the will’s papers that tell of an alleged treasure hidden inside the manor, but find the property haunted by a ghost named Casper and his poltergeist uncles the Ghostly Trio. They unsuccessfully attempt to force the ghosts out by way of paranormal experts and a demolitions team. A lonely Casper watches a news report about paranormal therapist James Harvey and is instantly smitten with his teenage daughter, Kat, prompting Casper to inspire Carrigan in summoning James to Whipstaff. Kat dislikes her father’s reputation and obsession with contacting the ghost of his late wife, Amelia. The Harveys move into Whipstaff, but Casper’s attempt to befriend them fails when his uncles try to torment and scare them away, which eventually fails.
Casper gains the Harveys’ trust when he serves them breakfast, and follows Kat to school, where she becomes popular when her class learns she is living in Whipstaff, and agrees to host their Halloween party. Her envious classmate Amber plots with her boyfriend, Vic, to humiliate Kat during the party. James attempts therapy sessions with the Ghostly Trio, who not only try to avoid them, but also reveal they know Amelia; in exchange for convincing Carrigan to leave them alone, they promise to go through the “red tape” involved to get James a meeting with his wife.
Kat learns Casper has no memory of his life, and restores his old playroom in the attic to remind him. Casper recognizes an old wooden sled his father bought him, and remembers playing outside until he caught a severe cold and died of pneumonia, becoming a ghost to keep his father company. A newspaper article reveals that Casper’s father was declared legally insane after he built a machine, the Lazarus, which he claimed could bring the dead back to life. Casper and Kat venture to the basement and find the Lazarus. Carrigan and Dibs sneak inside, steal the formula that powers the Lazarus, and plot to use the machine, believing it could grant them immortality. However, they attempt to kill each other to test the theory and retrieve the treasure they think is in the basement’s locked vault. This culminates in Carrigan attempting to run Dibs over with her Range Rover, only to instead crash into a cliff-side tree. Upon exiting her car, Carrigan falls to her death and becomes a ghost.
James becomes despondent after the trio pull a prank on him, prompting them to take him out on the town. They plan on killing him to make themselves a quartet but have a change of heart after the drunken therapist declares he will tell Carrigan off so they can stay in their home. However, James accidentally falls to his death down a manhole.
In the laboratory, a furious ghost Carrigan confronts Casper and Kat, stealing what she believes to be the treasure from the vault and launching Dibs out a window when he tries to double-cross her. As Carrigan demands to be brought back to life, Casper and Kat trick Carrigan into saying that she has no unfinished business on Earth, causing her to eject herself into the afterlife. After Carrigan’s ghost disintegrates and disappears, the chest she had been holding falls to the floor and the lid opens, revealing the treasure inside to be Casper’s prized baseball, signed by Duke Snider; the map was part of a game Casper played with his father. James, now a ghost, returns with Casper’s uncles, and Kat’s despair over this prompts Casper to sacrifice his one chance to return to life, restoring James instead.
The Halloween party kicks off upstairs; Amber and Vic’s prank is thwarted by the Ghostly Trio, and they flee in terror. Amelia, now an angel, meets with Casper alone in his toy room, crediting him for his bravery and sacrifice, and grants him a Cinderella-type deal that he can have until ten o’clock back as his younger, physical self, allowing him to attend the party and dance with Kat. Amelia meets with James and tells him that she was so content with her family while alive that she has no unfinished business, and encourages him to move on, while explaining that the Ghostly Trio kept their promise to get him a meeting with her. Amelia departs as the clock chimes ten, promising James that they and Kat will be together again one day and, after kissing Kat, Casper transforms back into a ghost, scaring off the guests. Kat nonetheless is impressed with the party, which James says is not over, cueing the Ghostly Trio to play their nephew’s theme for them to dance to.
A friendly ghost, well I’ll say. I loved this movie both as a kid and as an adult. Honestly the sequels are just as good and perfect for the Halloween/Spooky Season.