The last Grotto party was actually not bad for Calvin. His friends in Azurcrest are all going, and Ravi might be going too, so why not? He's still a little too awkward to suggest leaving with Pippa or Cole, although things between them aren't nearly as uncomfortable as they used to be.
So instead he bundles up and heads out alone. He knows no teacher would suspect Calvin Evercreech of being on his way to a Grotto party.