14-year-old Oliver Cates inadvertently transports Albert Einstein into the present with his computer. Before going back, Einstein helps Oliver work through his anger so he can reconcile with his mother, whom the boy blames for his parents' divorce.
Oliver has no one with whom he can share his secret, so he summons Alexander Graham Bell. However, his secret is uncovered by a curious 14-year-old named Dee Sampson who, thanks to Bell’s advice, Oliver eventually befriends.
Dee is upset by her parents’ investment in a toxic pulp mill, so she summons Joan of Arc to help organize a protest, despite Oliver’s reservations.
Dee’s reticence to leave her childhood behind motivates her to summon writer Lewis Carroll, whose real name is Charles Dodgson, who helps her deal with her grandmother’s death.
Oliver summons Napoleon Bonaparte to help inspire his pals to win a newspaper subscription contest.
Oliver thinks he lacks “the right stuff” where his father is concerned and, at the same time, his friend Bobby is being bullied by the football jocks. With the witty Oscar Wilde as their guide, they both learn that it’s okay to be themselves.
Oliver brings back Beethoven to help Dee deal with a pending operation that could result in her deafness. However, Beethoven is mistakenly brought back from a time when he isn’t deaf yet.
When Oliver plans on revealing his VisiCron technology to the world in return for fame and glory, Dee brings back the co-discoverer of insulin, Dr. Frederick Banting, whose own widespread fame in his day became nothing but an irritant.
Mrs. Tatlow, an impoverished senior citizen, refuses to accept the groceries that Dee has volunteered to deliver over the Christmas holiday. Undaunted, Dee gets a scrooge-like Oliver to call back the real St. Nicholas to help her deliver the goods.
Dee brings in Edgar Allan Poe to help make a Halloween fundraising event spooky, but Poe is charming and anything but scary.
Oliver wants to impress his father by winning a team “orienteering” contest: a race through wilderness terrain with only a compass and a map. For the team supervisor, Dee convinces Oliver to bring back Underground Railroad hero Harriet Tubman.
Dee convinces Oliver to summon Cleopatra to help her audition for a school production of Shakespeare’s Antony and Cleopatra. However, what she secretly wants is Cleo’s advice in winning the affections of school hunk Gino, who is auditioning for the part of Antony.
When Oliver and Anne get lost hiking in the woods, Dee brings back Daniel Boone to help track them down.