Bender and Fry are practicing magic tricks, when Fry spots a newspaper that claims people found 20th century artifacts. The two then visit the Museum of Natural History exhibit, where Fry finds out that it is actually Panucci's Pizza, the old pizza parlor where Fry used to work. Within the exhibit, Fry finds his old dog, Seymour Asses, fossilized and on display in the exhibit. After a lengthy protest, the museum gives Fry the fossilized dog. Fry starts to treat Seymour like an actual dog and Bender grows jealous of Fry's nonstop devotion to Seymour. At Planet Express, Professor Farnsworth reveals that he can clone a version of Seymour that Fry knew and loved. Just before Seymour's cloning process is completed, in a jealous rage, Bender throws Seymour's fossilized body into the lava pit in the basement. Hubert reveals that because Seymour was made of Dolomite, he might survive the hot lava. Bender, feeling remorseful and being 40% dolomite, decides to go after the dolomite dog. After a long while, Bender resurfaces with Seymour intact. While cloning Seymour the second time, Hubert reveals that Seymour was 15 years old when he died, leading Fry to think that Seymour must have lived a full life after he was frozen. Fry destroys the machine and leaves Seymour fossilized.
Throughout the episode, flashbacks are shown revealing how Fry and Seymour met, how they acted together and how Seymour lived after Fry was frozen. The final scene shows a slow and heartwrenching montage of passing years outside Panucci's where Seymour waits continuously for Fry to return (a reference to Hachiko, a dog who had a similar experience). Finally, Seymour lies down, closes his eyes and goes to sleep for the last time.
In a flashback to the night Fry was frozen, there is a short closeup on a waste bin in the cryogenics lab. Nibbler's topmost eye is visible among the discarded paperwork. This detail is explained in a later episode, "The Why of Fry". In the same vein, there is a second shadow below the table when Fry falls into the Cryotube, as opposed to only one in the Pilot episode.