Mary Beth is a museum tour guide who narrates the life story of Manolo's adventure and journey to a group of young kids who visited the museum. She is then revealed to be La Muerte in a human disguise.
Mary Beth wears a blue jacket over a white dress, a white bandanna on her neck, and black high heels. She has long orange hair, blue eyes, red lipstick, and wears small blue hat on the side of her head.
Mary Beth is a very kind lady and can be somewhat playful as she led The Detention Kids into the secret room.
Mary Beth was first seen outside the museum where she would take the kids on the Tour for Tomas, however when she heads up the stairs and doesn't go to the museum door, Sanjay pointed to where the door was but she said that they aren't like the other kids and wanted them to see something special she then leads them through an unseen door. One of The Detention Kids, Jane says that she's "seeing things", Mary Beth replyed back to her, " Am I or are you not seeing things?" by steeping into the secret doorway, the kids were amazed and proceeded to follow her through the hallway. As they are walking Mary Beth then tells them that it November 2nd which was Day of The Dead when suddenly a spooky guard appeared out of the dark scaring the children and said that they can't go this way but she was able to make him change his mind and give him a kiss on the forehead, they then continue down the hall, the guard scares Sasha and in a huge room, Mary Beth she shows them a book called The Book of Life, She began the story of Manolo and Maria,
Back in the museum, after Manolo's death, the kids were shocked even Sasha, Mary Beth bends onto her knees and told her that isn't over.