Grissom gets an invite to his highschool reunion but doesn't intend to go. Catherine finds out and convinces him to go with her has his date.

Must Have,
1. Without Grissom's knowlege Catherine tells his classmates that she's his wife.
2. Catherine pretty much tells one wopper after another to make Grissom (who was very unpopular in highschool) look good.
3. Someone hits on Catherine hard not believing someone like Grissom could get someone like Catherine.

Anything else is up to you.