In the film Now You See Him, Now You Don't, Dexter Riley is a student at Medfield College who is always experimenting with new scientific theories. One day, while trying to create a high-powered battery for his car, Dexter accidentally invents a liquid that can turn objects and people invisible.
Excited by his discovery, Dexter demonstrates the liquid to his friends, Debbie and Richard Schuyler. They quickly realize the potential of the invention and decide to keep it a secret. However, their plans are derailed when the greedy businessman, A.J. Arno, discovers what they have created and sets his sights on stealing it for himself.
Arno and his henchmen try to obtain the formula for the invisibility spray by any means necessary, leading to a hilarious game of cat and mouse between the students and Arno. The Medfield College gang is determined to stop Arno from using the spray to commit a bank robbery, but Arno is just as determined to get his hands on the invisibility formula.
Over the course of the movie, Dexter and his friends use their wits and cleverness to outsmart Arno and his cronies, leading to a series of comedic and exciting adventures. With the help of their invisible spray, the students find themselves in all sorts of outrageous situations, providing non-stop entertainment for the audience.
Now You See Him, Now You Don't is a fun, lighthearted comedy that combines science, mischief, and adventure. It is the second film in a trilogy of movies featuring Dexter Riley and his wacky inventions, which also includes The Computer Wore Tennis Shoes and The Strongest Man in the World.