All school kids have to graduate eventually and that time has rolled around at last for Richie, Potsie and Ralph. They are all very excited and thinking about college and their respective futures.
Quite by accident, Marion let's it slip that someone else is going to be graduating at the same time - none other than Fonzie! Fonz has been working extra hard to get all the necessary credit so that he can graduate at the same time as his friends and they are all very pleased for him but Marion is worried that Fonzie will be angry with her for letting the cat out of the bag as she knew he wanted to keep it a secret.
Not a totally terrible episode but like most graduation episodes on most shows, it's pretty predictable. I guess there isn't a great deal you can do with the format.