Gertrude Aldridge was the mentally disturbed daughter of the wealthy Sir Aldridge. Gertrude lived in the Aldridge Mansion with her wealthy father, until one day she went insane and murdered all of the Aldridge family's servants. Her horrified father locked her in the cellar, and kept her down there for the rest of her life, feeding her through a slot in the door. Years later, the Aldridge Mansion had changed hands until it belonged to Ed Mulgrave, Jr., who turned it into a haunted house style tourist attraction.
One night as tour guide Garrett was closing up, he heard terrifying howls coming from the cellar, and tried to flee, only for the doorknob on the front door to burn his hand. He tried to use a chair to break a window, but the chair was flung back at him, knocking him into the wall. Terrified, he fled into the cellar. Realizing his mistake, he tried to leave, but the old stairs collapsed under his weight, and glowing bluish-green ectoplasm began seeping up through the floor, before the ghost of Gertrude Aldridge herself attacked him. Garrett screamed.
The next day, Ed Mulgrave, Jr., having read a copy of Dr. Erin Gilbert's book Ghosts of Our Past, came to see her at Columbia University, hoping she could help. She along with Dr. Abby Yates and Dr. Jillian Holtzmann went to the Aldridge Mansion. Garrett, who'd survived his encounter with Gertrude, refused to go inside with him, giving them the keys and warning them darkly that they might die in there. Upon entering, Erin stepped in some slime on the floor and the cellar door opened. Gertrude floated out and confronted the three.
Erin's efforts to talk to her yielded no results. Suddenly, Gertrude transformed into a hideous, corpselike monster and vomited ectoplasm all over a terrified Erin before flying out the window. Later in the movie, during the Fourth Cataclysm brought about by Rowan North, Gertrude, along with Mayhem and the ghost of an executed murderer the Ghostbusters had encountered in the subway and failed to capture, confronted the Ghostbusters again, and this time they defeated her.