The show is a mish-mosh of Christmas traditions usually done to some theme - this year it is Medieval England. When I was in it in 1977 as a member of the Quadrivium, an early music performing group, it was French Medieval. It has carols, kids, a Mummers play, sword and/or morris dancing, other festive stuff and terminates with the whole audience getting up and dancing The Lord of the Dance out into the lobby of Sanders Theater in Memorial Hall at Harvard. That year there were I think 5 performances, now there are 19! That was a very busy year for the Quadrivium, I recall we had a performance or rehearsal every day from Dec 1 to Dec 21 either on our own in town or on the road or in the Cambridge and Dartmouth versions of the Revels. A couple of years later we did it again - this time an English version.
It's a pretty entertaining show, but when I went to it after having been it, I discovered it had been much more fun being in it.