Carol is sculpting a bust of Mike for her sculptor art exhibit, which is scheduled for that Saturday. So far, the likeness is not progressing very well and Mike is finding the sittings a strain.
That night, Cindy and Jan are woken up by a creaking sound from the attic. When they look out the window they see what looks like a ghost and start screaming. Their screams rouse their parents and Marcia. When Mike and Carol check the attic, they find the creaking was caused by a rocking chair. But they are puzzled as to the window being open. When they pass the boys' room they hear giggling and realize the truth - the boys were playing a prank on the girls. The girls realize the same thing and investigate the boys' room the following morning. They find that the ghost they saw was made by a slide in the family projector and a rope made the rocking chair creak. They swear revenge by scaring the boys with their own ghost.
At dinner, the girls pretend to be still scared by the ghost and will never go into the attic. They bet the boys would not do it either. The boys eagerly accept a bet that they will not stay the night in the attic, and their allowances are the stakes. The boys anticipate an easy bet and money while Alice, scoffing at the whole ghost business, calls it a sucker bet. Mike and Carol give realize what the girls are up to and brace themselves for "round two of the battle of the ghosts."
The girls strike with a tape recorder that emits a spooky voice and a ghost made out of cellophane rising out of the trunk. This scares Peter and Bobby out of the attic. Greg sees through the trick, but it is too late - Bobby and Peter fleeing the attic has caused them to lose the bet. The parents now decide enough is enough. Mike tells the kids that they are even and now they are not to scare each other. Carol warns the kids that a joke can go far and someone could end up getting hurt. The kids promise not to scare each other anymore.
Next morning, as the girls collect their bet, Alice scoffs over the "sucker bet", how anyone can be so scared, and brags she is not scared of anything. The kids decide to put this to the test by rigging another ghost scare, this time for Alice. They make the excuse to themselves that they only promised not to scare eachother and said nothing about Alice.
On Saturday night, Alice goes off on a date with Sam while Carol and Mike take the bust to the exhibit. While they are gone, the kids rig up their ghost gimmicks for Alice, disengage the lights for extra effect, and wait for Alice to return. They anticipate their parents will not catch them because they should not be home until long after Alice.
But the kids have miscalculated - the parents return before Alice so Carol can show off her ribbon; the bust won third place. The parents enter and find the lights not working. The kids, thinking it is Alice, start their scare tactics. The parents see through it immediately, and Mike goes to fix the lights so they can sort out the kids. But before the lights are repaired, Alice comes back. The darkness makes her confused and frightened at the sight of the bust. Mistaking it for a real person in the dark, she lashes out at it and breaks it. When the lights come on, the damage is evident. Carol is upset to find her prize-winning bust smashed to pieces and the kids are shamed. Carol tells them that she did warn them that someone could get hurt if a joke went too far. Mike tells the kids they will have no allowance for two weeks and sends them packing upstairs. Carol is even more angry when she finds the kids used one of her good sheets to make their ghost.
Next morning, the kids try to make amends by repairing the bust. The parents take the result in good part. Carol starts on a new sculpture, a Greek statue for the back yard. This time, Alice is the model.