Whoever Slew Auntie Roo?

Every year Auntie Roo hosts a lavish overnight Christmas party for ten well-mannered orphans in her mansion. Her warm demeanor masks a deranged state and the macabre secret she keeps in the attic—the mummified remains of her daughter Katharine. The festive setting foreshadows the danger lurking behind the party's gleaming surface.

Roo conducts regular séances to contact her dead daughter Katharine, with the help of the phony medium Mr. Benton who shares fees with the butler Albie. Clarine the maid also participates, using the dumbwaiter shaft to mimic Katharine's voice. The attic/nursery room serves as the stage for these deceptive encounters.

Christopher and Katy, two orphans, sneak into the party and are warmly welcomed by Auntie Roo when she notices Katy resembles Katharine. Roo's apparent kindness masks her fixation on replacing Katharine. The siblings become entangled in the mansion's dark affair.

After the party, Auntie Roo abducts Katy with the intention of using her as a substitute for Katharine. Christopher believes Roo is a witch who intends to devour him and his sister. His suspicion sets off a desperate bid to warn others.

Christopher tries to warn the other residents about Auntie Roo's plans, but no one believes him. Left with little support, he returns to the mansion to rescue Katy on his own.

Roo begins preparing a New Year's Eve dinner, continuing her ritualistic routines. Christopher helps by gathering firewood, unwittingly aiding in the later attempt to trap Roo. The tension inside the mansion escalates as the clock nears midnight.

Christopher and Katy steal Auntie Roo's jewelry and hide it inside an old teddy bear that belonged to Katharine. The stolen treasure becomes a potential future leverage for the children. Roo remains oblivious to the loss as she focuses on her next steps.

The siblings try to escape through the basement kitchen door but Auntie Roo locks them in the pantry. The claustrophobic confinement heightens the danger as Roo's attention returns to her abducted daughter.

Roo goes to the nursery to visit Katharine's mummy once more; this time the skull crumbles in her hands, shattering her fragile sanity. The moment underscores the futility of her obsession and its consequences.

Remembering what she overheard during the séance, Christopher has Katy call to Auntie Roo in Katharine's voice, which diverts her attention toward the pantry. This ruse buys a critical window for them to act.

Christopher hides on the top shelf and knocks cans onto Auntie Roo, toppling her to the floor. The siblings quickly lock the pantry door and seal it, turning the kitchen into a trap for Roo.

They place firewood around the pantry, douse it with paraffin, and set it on fire to ensure Roo cannot escape. They retrieve Katharine's teddy bear with the jewels and make their exit from the burning mansion.

Outside, Mr. Harrison the butcher arrives with a piglet, sees the smoke, and drives off to call the fire brigade. Katy realizes Auntie Roo was intended to cook the pig, while Christopher reveals they were to be eaten after the pig.

The fire brigade arrives but cannot rescue Auntie Roo, and Inspector Willoughby takes the children back to the orphanage. Christopher and Katy exchange relieved smiles, and the jewelry becomes their 'wicked witch's treasure' to secure a hopeful future.