Thrift shop owner Frank Standish is forced to take on a partner, Miss Moore. She immediately moves in and starts renovating the shop to make it more viable, and has a new doorbell installed. Frank tries to work in his back room shop despite the noise from the doorbell test, Miss Moore's dog Pookie, and the modern record she has put on. A neighborhood woman, Ellen Chase, comes in pulling a cart with two large packages on it. Frank leads her to the backroom workshop and serves tea, and they both talk about the old days and the first package, which contains a painting. The second item, a mirror, has been painted over and Ellen explains that it has been ever since she found it. She leaves them on consignment and Frank insists on giving her $10 for them.
As Ellen come out, Miss Moore is busy with a female customer. When Frank objects, he accidentally bumps the record player and the customer storms out. Miss Moore berates him for interrupting her sale and refuses to give him the $10 to pay Ellen. She does offer Ellen $1.50 for the cart, and Ellen reluctantly takes it out of desperation.
That night, Frank is working in his workshop when Miss Moore tells him that he'll have to find new quarters so they can convert the area into more floor space. Once she leaves, Frank scrapes off a bit of the paint and sees blue light shining through. He peers into the hole and sees a primeval landscape beyond the mirror. The next morning, Frank continues his work and shows Ellen what he's discovered when she comes back in. Once all of the paint has been removed, Ellen reaches her hand out and discovers that the glass is no longer there: the mirror is not just a window, but a gate. They see a path winding its way from the mirror to a cave in the side of a nearby mountain.
Miss Moore finally has enough and tells Frank that she's buying out his share of the shop, per their contract. She starts to pack away his equipment, and the elderly Frank admits that at his age he has little chance of finding work. Ellen wonders what he can do, and then notices a discarded ball that Pookie has dropped. She picks it up and throws it through the mirror. Miss Moore goes after her beloved pet and Ellen hands Frank a can of paint.
Miss Moore wanders through the jungle, following Pookie's barking. The dog takes refuge in the cave and Miss Moore goes to get him, only to realize that the dinosaurs that inhabit the landscape are closing in on her. She stumbles through the jungle, running back to the mirror, only to discover that Frank is administering the last few strokes of painting, closing the mirror-portal and cutting off her only means of escape.