Do you have anything prepared for this? Do you say, no but come back in a week?
Do you say, yes, here are four pre-gen character sheets, let’s play a random short one-shot?
Do you say, no we’d need to spend time prepping for D&D but here’s a simpler tabletop game which uses minis and dice, let’s play this right now instead? (for example, Shadowdark)
Or something else?
Hand them 4 pre-gens and run them through the Haunting for Call of Cthulhu. It’s made to be a pick up and play introductory scenario.