Through the adventure in summer, a boy experiences meeting and parting with a friend.

Nobita hatches an egg of Futabasaurus that is a genus of Plesiosaurs flourishing during the Cretaceous in Japan, named it "Piisuke". As Nobita, with getting a help of Doraemon and three friends, tries to send Piisuke to the place and period he should be, they face various difficulties.—tama