As someone inevitably said, "if today's so special how come there isn't a Doctor Who episode about it?" (No, this doesn't count.)
Which naturally lead to...
The Wedding Of The Seventy-Seventh Century
Somewhat inspired by this, steal more if you can. And by all the creepy political marriages in Game Of Thrones.
A wedding! And not just any wedding, the wedding of two of the great houses of the Third Great And Bountiful Human Empire, the sort of event that will alter the line of succession and, if it goes wrong, could plunge whole star systems into war.
So, naturally, someone wants it to go wrong.
Perception-altering assassins infiltrate the ceremony, there to target the bride, the groom, the bride's family, the groom's family, one of the guests, the officiator, another group of assassins who are targeting someone else, an incarnation of the Doctor who happened to pop by... could be just about anybody really.
(Alternative setting: any big politically-charged wedding, like let's say a royal wedding in medieval to Renaissance Europe. Consider any of Henry the Eighth's marriages and you've got six options right there. And don't mention Liz One's.)
Antagonists: Assassins who can look like anyone. But they can't do voices. And if they're in a hurry the scan can be one-sided and from an awkward angle and a bit distorted in the filling-in. And also whoever brought them here might have to be inside to give them a teleport signal to lock on to, so the mastermind might be here... or might have sent a flunky or duped someone into carrying the signal device or something.
Action Scenes: Laser battles around (and if we're doing this properly, on top of) the gilded carriage, chasing through the eaves of the abbey, runaway ceremonial horses.
Problems: Getting in might involve more than a quick flash of the old psychic paper. Unless, of course, you were invited... and if so, why? There's also the practical problem of an abbey full of powerful and important NPCs you might have to detail, some of which you definitely will.
Things To Prepare For: What else is going on in this meeting of the great and the good of this society? What other intrigues are going on, which might form subplots or provide red herrings? Do the couple even want to get married? What are the wedding customs of the 77th Century like? And what will we wear?
Continuing the Adventure: Lots of scope to complicate things, add more scenes, pursue the assassins through space and time with borrowed teleport gear, and most importantly comment on the peculiarities of some wedding customs.