I’m running Waterdeep: Dragon Heist so my idea is a burgler has stumbled upon a huge treasure in the basement of a manor… guarded by a dragon.
Game theme: Fantasy
The image that sums it up (and inspired it): https://vignette.wikia.nocookie.net/forgottenrealms/images/4/4a/Vault_of_dragons-5e.jpg/revision/latest?cb=20190310130537
The player: One very unlucky burgler
The goal: Escape! And hopefully with some treasure!