Larry Daly (Ben Stiller) seems to have a difficult life: he changes jobs frequently and has no fixed place to live; his wife divorces him, finds a stockbroker, and is about to remarry, and his position in his son's mind is also precarious. In order to save his life and to win custody of his son, Daly had to give up his dream of "doing big things" and became a night guard at the New York Museum of Natural History. Daly originally thought it was a boring job, but who knew that on the first day of work, something incredible happened: the Pharaoh's gold medal in the museum has magical powers. When night falls, all the specimens in the museum will come alive, the Tyrannosaurus Rex chasing bones, the monkeys who love to make trouble, the tyrannical Hun King, the cavemen who drill wood to make fire... everything will be out of control. With the help of the 26th President Teddy Roosevelt, Daly finally controlled the situation, but he immediately encountered new troubles: someone wanted to play the Pharaoh's gold medal. Daly had to stand up for his duty and for the miracle of the museum at night.