At a college campus, Professor Walter Jameson is lecturing a class on history. He talks about the Civil War and the Union soldiers burning Atlanta on the orders of General Sherman. Jameson reads from the diary of a Major Hugh Skelton. In the classroom is 70-year-old Professor Samuel Kittridge.
That night, Jameson goes to the wife of his fiancé Susanna, Samuel's daughter. He's unaware that an elderly woman is watching him from the shadows. Jameson, Samuel, and Susanna enjoy supper while Samuel insists that his daughter study and get her PhD. After she leaves to study, Jameson sits down for a game of chess with his friend. Samuel asks how hold he is and Jameson says he's 44. Upon hearing the answer, Samuel notices that it doesn't correspond with what his college application says, and that he should be 51. Jameson admits he lied but Samuel doesn't drop the matter. He notes that Jameson hasn't aged at all since he's known him in the last 12 years. Samuel notes that some of the students say that Jameson speaks of historical events as if he lived them.
Samuel goes to the bookshelf and takes an album of Civil War photos. He finds a picture of an officer that looks just like Jameson. Jameson says he didn't have any relatives in the Civil War. Samuel shows him the book and the photo of Hugh Skelton. He's an exact twin of Jameson. Jameson tries to deny it but Samuel points out Jameson and Skelton have the same mole and the same ring. Samuel demands the truth and Jameson finally admits that it's true. He points to a statute of Plato and admits he knew him personally, over two thousand years ago.
Samuel asks how it happened and asks for the secret. Jameson explains that he can't. He was afraid of death and sought out an alchemist, who experimented on him and gave him immortality. However, Jameson soon realized that everyone he ever grows close to die while he continues on without aging. Samuel thinks anything would be better than dying, but Jameson admits that it's death that gives life its point. He admits that he's still a coward and can't bring himself to use the revolver that he keeps in his desk.
Samuel realizes that Jameson is correct and asks if he's been married. Jameson insists that he tried to keep Susanna from falling in love with him, and finally he came to love her as well. Samuel says he won't let Jameson marry his daughter. Overhearing the last few words, Susanna comes in and demands to know why her father feels that way. Jameson asks her to marry him that very night. As she goes to pack, Samuel threatens to tell her but Jameson says that nobody will believe him, and Samuel won't believe it by the next morning.
Jameson goes home to pack and sees the gun in his desk drawer. He contemplates it for a moment and then puts it down. The woman from the shadows, Laurette Bowen, is waiting for him. She calls him "Tommy" and prods him into remembering her. He tries to deny it but she says that he's her husband and saw his picture in the newspaper. Laurette realizes that he'll marry Susanne and abandon her, the same way Jameson abandoned Laurette. She picks up the gun and shoots him, saying he can't go on hurting people. A shot rings out and Laurette leaves.
Samuel hears the gunshot and runs over. Jameson tells him that he's come to his senses at last. Samuel tries to call a doctor but Jameson stops him. Samuel looks at his friend, who is aging by the moment. With a last expression of relief, Jameson collapses to the floor, aging rapidly. Susanna runs toward the house and Samuel goes out to stop him. She shoves past him and enters Jameson's study. However, there's nothing there but an empty suit of clothing and a pile of dust.