Cat's family had to move towns for Cat's sister, Maya. Maya has a health condition that makes it hard to breathe. There they meet a boy named Carlos, and he wants to take Cat & Maya on a ghost tour.
On the ghost tour, Carlos explains that on November 1st they celebrate ones that have passed, and their ghosts come "back to life". Cat doesn't believe this and wants to see proof. So Carlos takes them to a mission.
On the way to the mission, the weather gets colder and the air gets thinner. At first, Cat can't find her sister or Carlos. She walks around the abandoned place and sees ghosts around her sister who is on the ground coughing. When Cat reaches her she knows she has too call 911.
When Maya finally gets back from being in the hospital Cat knew it was a mistake to take her to the mission. Unfortanly Maya can't go trick or treating or go to the day of the day party with Cat and her friends.
On Halloween Cat gets picked up by her friends and goes trick or treating and after to the day of the dead party. It's pretty lonely without Maya. But then she meets Carlos's uncle and he gives them a ride back home to Maya.
At home Maya and Carlos's uncle play, and then have to leave. Once they do Maya and Cat go into the kitchen and see a table of food sent up for them. They think that maybe their late grandma made it for them. So without hesitation they eat the food in mind of their grandma.